Document oD8KrLLOQBqEgnoMnqrxxpJQE
35.
TALE 7
Number of Person* and Number of Lung Cancer Deaths by Length of Employment
Length
Asbestos
Thetferd Minos
Combines
of
Lung Cancer
Lung Cancer
Employ*
Cancer
Deat hs
Dtuhs
men: Persons Ceatns Persons Proves Total Persons Provec Total
5*9 10*19 20*2 aO-39 40*49 iC* Tot 41
880 964 342 168
IT 2
Tm
0
915
0
0
1534
1
1
56C
2
2
435
3
0
166
0
0
53
0
T
3oa5
7
0
1795
0
0
1
2396
1
1
2
922
3
3
5
603
5
?
1
185
0
1
0
55: 0
0
9
7557
9
71
Annual Lung Cancer Dea:h a;c* per 100, OCC M4A*Y*4rs of Exposure by Length of Employment
Length ef Employment
5-9 10*19 20*2 30*3 40*4 SO* Over.*11
Asbestos Total
0 0 49 196 0 __0 22
Thettord Mines Proves Total
0
0
U
11
57
57
115
192
0
99
0
0
27
41
Combi ned Proves Iota.
0
0
7
7
34
54
138
193
0
90
0
0
25
34
0170
39.
TAB-2 6
Number of Persons and Number o' Lung Caneer Deaths by Exposure Category
Expos* urc
Cate* torv
Asbestos
Thetford Mines
Combined
Lung Cancer
Lung Cancer
Cancer
Deaths
Deaths
Persons Deaths Persons Proved Total Persons Proves Total
1
969
2
1062
2
2
2031
4
4
21
564
1
1506
2
3
2150
3
4
111
735
0
1037
2
4
1772
2
4
Unimows
$
0
0
0
0
SO
0
Total 2273
T
3663
6
9
595S
9
12
Annual Lung Cancer Death Rates per 100,000 Man-Years of Ex posure by Exposure Category
Exposure Caterer*.-
Asbestos Total
1
34
I
22
30
m
0
Ualetewn
0
Over-all
22
No one exposed
Thetford Mines proveo Total
31
31
22
32
32
64
0
27
41
Comb: r.ed Proves Iota.
33
33
23
31
19
37
0
0
25
34
0171
40.
U exposure 10 asbestos ;s ar.y way connected to lung cancer. we would expect that tbt longer and heavier the exposure, the higher the rate that would he found. The only possible error us this interpreta tion could occur if the weighted exposures were inversely related to years of employment, in which case the heaviest weighted exposure (category HI) would show the shortest length of employment. Tables 9, 10, and 11 which list the number of persone in various exposure categories by length of employment indicate that this error has not occurred. In fact, the average number of years of employment for each exposure category is almost identical.
TA8Le 9
Number of Persons m Verious Weighted xposur Categories by Length oi employment
Asbestos
Length of CmotO'.mer.t
S-9 10-1? 20-29 30-3* 40.4; 50 Tout Av. Yrs. of Lapcsure
Weighted exposure Catercnes
I
U
m
428 273 159
98 9 2
56? 15.6
213 21?
89 42
3 0 504 15.2
239 373
92 2?
4 0 735 14.5
Unknown
0 l 2 1 1 0 * s 29.0
Total
880 164 342 168
1? 2
2272 IS. 1
7
0172
/
4;.
TABLE iO
Number o i Per ton* uv Viriou* Weighted Sxpoture Cetegones by Length of Employment
Thetferd Mines
'Length of Emeloxment
5-9 10*19 20*29 20*39 40*49 50 Totei Av. Yrs. of Exposure
Weighted Exoosure Ceteeories
i.
JL
ML
279 390 155 149
6? 22 1062 19.9
385 666 274 176
64 21 1556 18.7
251 478 151 no
3? 10 1037 18.1
Unknown
0 0 0 0 0 0 - `0
Totel
91$ 1534
580 435 168
S3 3665 18.9
TABLE il
Number of Persons m Venous Weighted xpesure Cetcgarset by Length of Employment
Combined Asbestos end Thetiord Mines
Length of Emolevment
5*9 10-19 20-29 30*39 40-49 50 * Totel Av, Yrs. of Exposure
Weighted Exposure Ceteserics
1
U,
1U
707 663 3M 247
76 24 2031 17.6
598 883 363 218
67 21 2130 17.8
490 851 243 137
41 10 1772 16.6
Unknown
0 l 2 I 1 0 5 29.0
Totel
1795 *2398
922 603 185
55 5958 17.5
17
4i.
Table 12, which develop* the rates for smokers and r.on-
smoktrs, is most striking. It shows that no: a *;r.;lc case of lung
cancer developed among the 1265 nonsmokers and that all cases of
lung cancer, both "proved" and "suspected", occurred ui smokers.
A comparison of Tables g and 12 certainly suggests that smoking is
a greater haaard than exposure to asbestos in the mining operations.
Table 12 was so striking that it was felt that further veri
c
fication was necessary, it was possible that some abnormal distri
\
bution may have occurred, e.g., the nonsmokers may have included
a larger percentage of young men. Consequently, additional Tables.
15, 14, and IS were eonstructed to show the distribution of smokers
and nonsmokers by age, length of employment, and degree of exposure.
Although there are slight differences, they do not account for the fact
that all observed eases of lung cancer were in smokers. In respect to
age (Table 15) the combined average age of the smokers was 4.9 years
less than that of the nonsmokers. Table M shows that as far as length
of employment is concerned, the smokers had worked about 2.5 years
less on the average than the nonsmekers. With longer exposure and
greater age, one would expect the nonsmoking group to show a higher
rate if lung cancer were due to asbestos.
Table 15 shows that the average exposure category was al
most the same for tbe two groups. Therefore, this variable seems to
be of no importance in accounting for the difference between lung cancer death rates for smokers and nonsmokers.
0174
f l
43.
TABLE 12
Number of Persona and Number of Lung Caseer Deaths by Smoking Habits
Asbestos
Tbetford Mines
Combined
Lung
Lung Cancer
Lung Cancer
Cancer
Deaths
Deaths
Persons Deaths Persons Proved Total Persons Frovd Total
(
Smokers
1931
3
2742
6
9
4673
9
12
Nonsmokers 340
0
925
0
0
1265
0
0
Univows
2
0
U
0
0 . 20
0
0
Total
1273
1
3685
r
S95&
9
12
Annual Lung Cancer Death Antes per 100,000 Man-Years el Exposure by 5mokiSg Habit*
r
)
Smokers
SK,':
]
Nensmokcrs
A
Unknown
\
Over.all
i
Total
26
0 0 12
Thetford Mine* Proved Total
36
55
0
0
0
0
17
41
Combined Proves Tou
32 43 00 00 25 34
0175 1
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0178
Tbe result of this addition*; analysis is that none of these factors appear to lessen the effect of Table i*. which ;s therefore strongly suggestive of the importance of smoking as compared to the other variables.
Asbestosis and Lun- Cancer
When w attempt to relate the lung cancer deaths occurring
in the cohort with the reported cases of asbestosis, we are immediately
aware of a disturbing inconsistency. Various authors report tbe incidence
of asbestosis after 10 or 15 years of exposure as exceeding 50%, and ;r.
one study, as high as 6~%.
However, data on
cases of asbestosis from the cohorts at Tbetford Mines and Asbestos pro
duce a rate of only about 5%. It is true that these data are based on only
those cases whieb have been proved at autopsy, and those whose most re
cent x-ray interpretation resulted in a diagnosis of asbestosis. This in
cidence may be far lower than if based on microscopic examination of the
lung tissue. As a matter of fact, Or. Cartier has estimated that there are
probably 300 workers who do not show radiological evidence of asbestosis,
but who have some degree of fibrosis. He also estimates that there arc
perhaps 40 workers who may have died or retired with this disease. Instead
of M3 cases of asbestosis m the whole working force at Tbetford Mines,
we should then have perhaps 500, but even this would result in an over-all
rate of less than 10%, which is far below those widely reported. In our
0179
\
48
combined conort, there ire 1765 men who hive hid mere than 12 ytinjl employment, ad 431 of the** hive worked in the heavies: average exposure. According to the records, we can account /or only 136 cases o/ asbestosis is the combined cohorts. 1/ even 25% o/ the workers with more than 20 years1 exposure develop asbestosis, we should expect about 425 cases. Tb* leads us to believe that there is a very coasiderablc under-reporting of asbestosis. Such a hypothe sis is easily conceivable when one considers that many chest x-rays in this group may be considered normal by comparison with others
\
in the same group whereas, if they were to be compared with wba: are considered ss normal chest x-rays elsewhere, they may be inter preted as showing fibrosis.
Cases of asbestosis which were accumulated from the au topsy records and from the periodical physical examinations result m a distribution which is shown in Table 16.
TABLE 16 Distribution of Recorded Asbestosis Cases
In Cohurt
Living Deae
Total
Asbestos
16 4
22
Tbet/ord
66 30 116
Combined
104 34
136
/
49.
TAB1 17. Pin 1
Narbr of Asbcstaxis Casts By Length of Zrapioyme.nt and Exposure Category
Asbestos
.Length of molo\meat
Less than 10 10*19 20*29 90*39 40*49 SO + Total
Av. Yrs. of mplo>eaj
Exposure Catecorv
ui
0
0
0
0
1
2
2
7
4
0
i
4
0
0
1
0
0
0
2
9
n
2S
25
29
UfUCtOW?.
0 0 0 0 0 0 0
Total
0 3 n 5 l 0 22 2?
Percentages of Asbestos!* Casts By Length of Scspiayrsoat a&4 Exposure Categ sry
Leagtb of Cmolovrr.tTs.:
Loss than 10 10*19 20*29 90*39 40-4 SO Oversell
xeosure Cates erv
i.
u_
U1
0
0
0
0
.5
.5
2.3
7.9
4.3
0
2.4
14.8
0
0
25.0
0
.2
1.6
l.S
* No one exposes is this grow?
Unknown
0 0 0 0
T
Tots;
0 .3
3.8 3.0 5.9 0 1.0
0181
so.
7A2LZ ;? . Pin L
Number of Asbestosjs Caaes By Length of Employment and Exposure Category
Thetford Mists
Length of Emelevnent
tut thin 10 10.19 20-29 30.39 40-49 SO Total
Av. Yrs. of Employment
Exposure Cateeorv
I
ii
HI
0
0
0
0
1
7
2
s
21
2
IS
33
0
6
20
0
2
2
4
29
63
30
36
34
UnJejown
0 0 0 0 0 0 "0
Total
0 6 28 SO 26 4 116 34
Percentage* of Asbestos:* Cates By Length of Employment cnc Exposure Category
Length of Employment
Lnemt Cat esorv
1
III
Less than 10 10.19 20.29 30-39 40.49 SO * Over-aii
0
0
0
.2
1.3
1.8
1.3
8.5
0
9.4
0
9. 5
. 4
1.8
* No or.c exposed in this group
0
l.S
is.9
30.0
S4.1
20.0
6.0
Unknown
0 0 0 0
T
Total
o .5
4.8
11.S 1S.S
7.S
3.1
0182
SI
TAB LZ 17- Par: .12
Numb*; of Atb*stasis Cases By Length 0/ Employment end Exposure Category
Asbestos and Thetlord Mines Combined
Length of EmoJevmer.t
Lot than 10 10-19 20-29 )0.39 40.49 SO Toul
Av. Yrs, of Employment
Cneturt Cateeorv
JU
_ 112
0
0
0
0
2
9
4
12
2S
2
u
3?
0
6
21
2
2
6
35
94
25
33
33
Unknown 7oul
0
0
0
11
0
41
0
s$
0
2?
0
4
0 t - 136
33
Percentages of Asbestos*.* Cases By Length 0/ Employment ane Exposure Category
Length of Emolovmer.t
Exooswre Catecorv
Jl
m
Less than 10 J0.J9 20.29 30.34 40*44 SO Over-all
0
0
0
0
.2
1.0
1.3
3.3
10.3
.#
7.3
27.0
0
9.0
$1.2
0
. i
20. 0
.3
J.S
S. 3
* No one exposed in this group
Unioown
0 * 0 0 0 6
Total
0 .5
4.4 9.1 14.6 7. 3 2.0
0183
3 2.
A percent*^ incidence of
:'or t*ci exposure
category has ttt: ceve.cpec a* well j for each pence c; empicy-
mest. This uueraettsn is shown in Table 1?.
It will be noted that wuhin an exposure category, the
incidence rises with increased length of employment. It is also
apparent that the incidences, even in the category of heaviest ex
posure, are far below the rates found by tbe authors previously re
ferred to. It seems clear, that unless concentrations of asbestos
dust to which the miners are exposed are very much lower than those
which ostein in all the other stuctcs, there has been a'gross under
reporting of tbe asbestesis cases. The obvious result is a higher
relative frequency of lung cancer is association with asbestosis.
Table 18 compares deaths due to lung cancer ana fatal cases with as
bestosis, alone and m combination with each other.
TABLE 18 - Part 1 Statistical Analysis of the Causes of Death
Asbestos
Cause
Asbestosis No Asbcstosts Total Percentage
Lung Cancer
| { .2)
2 ( 2.8)
3
8.1
No Lung Cancer
3 (3.$)
^(42.2)
j46
3.9
Total
T
4S
44
Percentage
8.2
91.8
Figures in parenthesis are the "expected" numbers
0184
i~C~
53.
TAB^ 18 . Par: 11 Statistical Analysis of the Causes of Death
Thctford Mines
Cause
Aibotam No Asbestasis Total Percentage
Lung Cancer
3{ 1.3)
3( 4.7)
6
No Lung Cancer
,25(26.7)
101(99.3)
126
Total
28
*104
132
Percentage
21.2
75.5
4.5 95.5
figure* ia parenthesis are the "expected" number*
TASL 18 - Part 11
( `
Statistical Analysis of the Cause* oi Death
Asbestos and Taetiord Mine* Combined
Cause
Asbestosii No Atbestar.* To1
Long Cancer
4 ( 1.5)
5{ 7.4)
9
No Lung Cancer
^8(30.4)
144(141.6)
172
Total
32
149
151
Percentage
17.7
52.3
Figures in parenthesis arc the "expected" number*
Sin death* from unknown cause* not included
Percentage
5.0 95.0
Tbe number of lung cancer deaths combined with asbesiotis
is larger than would be expected in eaeb cohort and m the combined
cohort*. This difference is significant at the 55% level using tbe chi*
square test of significance. Tbe importance of tbe under-reporting of asbestos:* caa be observed in Table 19.
0165
Statistical Analysis o: the Causes o( Death if 20 Nonasbestosis Cases bad been Diagnosed aa Asbestosi* Caaea
Cauae
Asbc*to; No Asbcstosis Total Percentage
Lung Cancer No Lung Cancer
Total Percentage
4{ 2.6)
5 { 6.4)
48(49.4) 124(122.6)
52
m
121
22.7
7X.3
5.0 95.0
Figures ia parenthesis are the "expected11 numbers
\
la tbia table, it baa bees assumed that 20 o the caaea which did aot have luag caacer aad which were reported to have ao esbeetoais did. in fact, have aabcatoeia. the diagnosis of which waa missed. Although the caaea of luag caacer with aabeatoaia are still higher than would be expected, the difference is ae longer significant at the 9S level. This still ia true if fewer than 20 eases were shifted but it ts reaaoaable to expect that at least 20 of the 144 might have shown asbestoais bad they been aubiect to autopsy. On the other band, a shift of about 40 caeca would produce an expected rate almost equal to tbe rate found. Explanation of this effect of uader*rcportmg of as* bestoaia baa been stressed because t seems ao obvious that ia under* reporting asbestos;* tbe relationship between it and luag cancer has been made to appear more significant than it probably is.
I
i
i
* i
Four of the proved eases of lung cuter *rc see of the
suspected were associated w;:h asbcstasis. Since w hove only 32
deaths in which asbestosi* ws* present according to tbe records,
the incidence in this eerie* i* 12.5%. wnilc this i* slightly fewer
than the rate* found by Merewetber, Gloyne, and WedJer, it i* still
aueb bigber than could be expected if the asbestosi* incidence were
anywhere near tbe experience reported by other author*.
c
*
Comsar:on of tbe Cohort xserience with that of tbe
'
Province of Quebec. Dominion at Canaoa, ar.c the Unites State*
i
la order to make a comparison of tbe experience among
asbestos miners with that of tbe general population of the Province of
Quebec, autistic* were gathered, as stated earlier, in tbe office of
tbe Division of Demography in tbe Provincial Ministry of Health. The
data on total deaths, deaths from all forms of caneer, and deaths from
cancer of the lung were obtained by sex and by eounty for the years
1950 through 1955. In addition, all death certificates which specified
primary cancer of the lung, and all those.which indicated lung cancer
but did aot specify the origin, wre examined for the years 1952 through
1955.
Table 20 gives a tabulation of tbe number of detti* from
lung cancer in the Province ana in the two cohorts for-the years 1950
c
through 1955, and show* the annual rate per 100,000 in these segments.
0187
Restricted Copy ^31.
")
CONFIDENTIAL
1 PLAINTIFF'S^
(t EXHIBIT
j Xttf 77
INDUSTRIAL HYGIENE FOUNDATION OF AMERICA, INC. 4400 FIFTH AVENUE
PITTSBURGH 13, PA.
AN EPIDEMIOLOGICAL STUDY OF LUNG CANCER IN ASBESTOS MINERS
Report to QUEBEC ASBESTOS MINING ASSOCIATION
Quebec, Canada
September, 1957
(50 Copies Reprinted January 1980)
'jLScaJ
Induatnal Hygiene Found. 'ion x Amenci, Inc. 4400 Fixth Avenue
__ Pittiburch ;j, p*.
geft>cr Tt-tesofei-i-
IZT-
AN EPIDEMIOLOGICAL STUDY OF LUNG CANCER
IN ASBCSTOS MINERS
For
QUEBEC ASBESTOS MLNING ASSOCIATION
-
Quebec, Canada
July, 1956 to July, 195?
By
Daniel C. Braun, M.D, Medical Director
September, 195?
By: C. Richard W.\imer, M.D. Managing Director
oizr<
TABLE OF CONTENTS
Pege
Foreword.....................................
i
Cloutry................................................................................................... ir
1. Introduction..............................................................................................
I
S. Criticel Review of Literature..................................................................5
III. Principle* of the Eplatraialogical Method ....... 1S
IV. Collection end Analyst* of Oete.................................................... 18
V. Result* end Interpretation.......................
28
Aebestoeis end Lung Ceaeer. ................................................. 47
Comparison of the Cohort Experience with thet of the Province of Quebec.
Dominion of Canada, end the United States..........................55
Comparison Between Eight Countiee Adjacent to the Asbestoe-Preducing Arcee end Eight Selected Countiee....................................... 86
Discussion of AU Recorded Lung Cencer
Cases, Living end Deed, et Aebeetoe end
Thetforo Miner................................................
68
VI. Summery end Conclusion* ...................................
71
VU, Bibliography......................
78
0128
FORWORD
The success of & study of the type herein reported deRends very greatly upon the availability of dsts from many sources, end the assistance and cooperation of those in possession of these data. Industrial Hygiene Foundation woo fortunate in having the wholehearted cooperation of the asbestos-producing companies, and particularly of their medical and nursing personnel who have the re sponsibility for maintaining the medical records of the workers, In this connection, we are especially indebted to Dr*.aui Cartier and his staff at the Thetford Industrial Clinic, and to Dr. T. ft. Grainger and the nurses at Asbestos. All records in these two medical cen ter! wore put completely at our disposal, and the eare and completesees with which they are maintained assisted considerably in the preparation of the material relative to the worker population.
Data on population figures and on the causes of death in the Province of Quebec were obtained with the utmost assistance and co operation from Dr. Paul Psrrot, Head of the Department of Demogra phy in the Ministry of Health. Not only were all vital statistics and reports made readily available to us, but Dr. Parrot and bis entire staff rendered valuable assistance in many ways, including thr location and interpretation of death certificates. specially helpful in this part of the work was Miss Gauthier of Dr. Parrot's staff. The same helpful
0129
cooperation was rendered by Messrs. Hardy and Hopkins of :fae Sun Life Assurance Company of Canada in Montreal, who made available their record* of the deeth claims pAid under the group policy cover* ing the worker* At Asbestos.
Valuable suggeation* for the conduct of the study were mode by Or. J. A. VidAl, Chairman of the Silicosis Boord, AAd Or. Cuy, Pathologist for the Boord, as well as Or. Cregoire, Deputy Min* ister of Hesith for the Province of Quebec, And Or*. Simard, Oufresne,
f
And Groulx. in MentreAl. Statistics for the morcAiity rAtes for the Dominion of Canada
were obtained through the kindness of Dr. D*aa T. Davies, Admiaistra* tor for Beeearch on Lung Cancer for the American Cancer Society, And those for the United States were grsciously furnished by Miss Curainick in the NAtiennl Office of VitAl StAtistics, Department of Health, Education. And WelfAre of the United StAtes Government. Finally, the very greAt Assistance rendered by Or. Kenneth W. Smith, MedicAi Director of Johns* Manviile CorporAtion, end Mr. Ivan Sabourm, GenetAl Counsel for the AssociAtion, in making the necestAry centActs, in travel arrangements. And m so many other wAys, is grAtefully Acknowledged.
The methodology of this research is believed to be un.que among the reported studies of lung cancer as related to asbestos;* and exposure to asbestos. Assistance in planning the study in such a way as
0130
//
in. to itturt 4 proper epidemiological approach, end *11 biostitistica! Applications of the ftnoings were provided by Mr. T. Davie Truan, formerly of the Graduate School of Public Health, University of Pitts burgh, and the staff of the Industrial Hygiene Foundation.
The report is believed to present the findings in an objec tive manner and is respectfully submitted for the consideration of the Aseoeiation.
,/
\
\
Hi
l
IV.
I -
GLOSSARY
For the purpose of clarity end uniformity, the terst used in this report ere herewith defined according to the manner of their use.
: *r*fT. <A -'
Asbestos workers:
Workers exposed to asbestos dust in other than mining operations.
Asbestos miaers:
Workers engaged ia the
and prepare*
tioa of asbestos ia the areas uader study.
Asbestosis:
A generalised fibrosis of tbe luags diagnosable by x-ray, or by microscopic examiaatioa of the luag tissue, hut not necessarily accompanied by symptoms or by disability.
Cohort:
A segment of the population, defined accord*
-
inf to eertaia criteria, and representative of
the whole population. Specifically ia this
study, a group of asbestos miners hiving at
least five years of exposure in the iadustry
and who were ia the industry during 1950.
Luag cancer, cancer of the lung:
A neoplasm of the luag or bronchus, wher ever situated, and including adenocarcinoma, squamous cell, and undifferentiated, round, or "oat cell" histological types. Primary cancer of the luag mesas such a neoplasm originating ia the lung, and not secondarily in the lung as tbe result of * metastasis from another primary location in the body.
Smoker:
As used in thie presentation, the term smoker refers to s cigarette smoker, habitually smok ing more than five cigarettes per day. Persons who smoke pipes or eigars exclusively were net considered to be smokers tor the purpose of this study.
013
I. INTRODUCTION
Ever since the pronounced increase in the incidence 0/
lug cancer among males btcamc apparent, there have been attemptj
to uiocuu it with one or another of the various element* in the en
vironment of man. The approach need by tome worker* ha* been to
suspect one or several substance* and then set about is an intensive
search for lung cancer among persons who have had any exposure to
those compound*. la this connection, Smith
writes; "The ten
dency of anthers reporting the coincidental occurrence of primary
lung cancer with silicosis or with any other theoretical etiologic con
ditions, has been to emphasise the percentage relationship in extremely
stall series of eases, with control cases which are not in any way
comparable."
It would eeem inevitable that aebestes should com* under
scrutiny in this manner, because prolonged exposure to this material is
known to cause a specific type of pneumoconiosis, and because persons
who show this form of patumceoaiosis often come to autopsy and pro
vide a ready source of material for study. It was in this way that re
ports of the simultaneous occurrence of lung cancer and asbestesis be
gan to accumulate after the report of a ease by Lynch and Smith
in
1935. Within the next ten years, about 15 additional cases were reported,
aod in 1996 Merewstber
reviewed all deaths from asbestesis re
corded in England since March, 1929. Lung cancer occurred, according
013:
2
to Mertwetber, m 13,2% of these cases. Continuing this study to
include December, 1954, Merewether counted 55 cases of cancer of
the lung Among 344 esses of asbestosis, raising the incidence to 16%.
(92}
Cloyse,
whose work is also frequently referred to it establishing
i connection between isbestosis and cancer of the Lung, reported in
1951 the results of his findings on 1205 autopsied cases. This series
included 152 asbestos workers, of whom 121 showed isbestosis. Cancer
of the lung wis present in 14.1% of these asbestosis cases. In 1941,
Nordmana and Serge
claimed to have produced lung eaneer in mice
which they exposed to asbestos dust.
Since 1951, additional cases of cancer of the lung coexisting
with asbestosis hive been reported, and, accorcmg to Hueper
about
100 such cases had been reported up to 1955. As a result, an associa
tion between the two diseases appears to have been accepted by miny
authors and several writers were using the term "asbestosis cancer" of the tang. Werber ' ^ in 1952, stated categorically that in 7% to 17%
of cases of asbestosis, after a latent period of about 1 1/2 to 20 year*, carcinoma becomes established in tb* lung.
On the ether hind, net ill lutbore accepted the alleged associa tion without reservation. Saupe ^ ^ in 1939 hid reported that be hid
discovered no cases os' lung cancer among 620 cases of asbestosis wbieh
he had examined; and in 1942, Kolleb and Angnst
expressed the
opinion that thv number of eases of asbestosis with lung cancer was too
0134
j.
small {or statistical evaluation. In 1947, Wegelius '
reported 126
rAdtolegicAlly eiagr.osed cases of asbestosts Among 476 workers in
fuuand, <>nd found no cases of lung cancer in this group. ColdblAtt
And ColdblAtt :n their section of Merewether's lAtest book,
stAte:
"But At no stAge in All these impressive resesrehes was
Any clue obtAined which might hove offered Any support to the possi
bility that Asbestos could act as a carcinogen. There is no reliable
criterion by which one can anticipate carcinogenicity and, as is well
known, relatively minute changes in the structure of a chemical car-
cinogen are sufficient to diminish or eliminate carcinogenic action.
If asbestos is indeed to be regarded as a carcinogen, the
need is felt to demonstrate some property which ean be regarded as
something more than inertness."
These authors advance the theory that, until some more
experimental evidence of direct carcinogenesis by asbestos or a de
composition product of it ean be obtained, asbestos might be considered
as a "co-carcinogen" which only induces a further development of a pre-
neoplastic condition brought about by something independent of the as
bestos, such as an endogenous factor.
Thus the literature, while tending to support the thesis that
asbestosis is in some way related to the development of lung cancer, is
by no means unanimous. Altogether, it is perhaps more confusing than
enlightening.
4.
Meanwhile, the Canadian Johns-ManviUe Company in Asbestos nas been a-ert to the whole problem, and at the Tbetford Industrial Clinic. Dr. Paul Cartier was studying the situation among a working population 0/ about 6000, and made notable contri butions to the literature just cited^**^. Between these two artas, a number of cases bad been recognised and tabulated by the spring of 1956. At this time, at the suggestion of Or, Kenneth VV. Smith, Medical Oireetor of the Johns*Manville Corporation, and Dr.Cartier, the Quebee Asbestos Mining Association approached Industrial Hygiene foundation to determine whether it would be feasible to conduct an epidemiological study in order to discover whether the incidence of lung cancer was, in fact, greater among asbestos miners than among te general popuia* lion, and whether there was a correlation between lung cancer *nc the disease asbestos;!. The foundation submitted, m March, 1956, a pro* posal for such a study based upon s preliminary survev of the type and accessibility of data wbieh might b< available. This proposal was ac* cepted by the Association through its Secretary, Mr. IV. H. Sogtar, and its General Counsel, Mr. Ivan Sabourin, *4.
015;
//
XI. CRITICAL REVIEW or LITRATUR
A careful review of the published material on this ub*
jet shows that the majority of the reports are clinical and not epi
demiological. They lack many elements necessary lor the applies*
ties of epidemiological techniques-to their eontent and most of the
authors do net make claim to Having done so. What has happened
(
is that succeeding authors have drawn conclusions and generalised
beyond the scope of the works which they quote. Nowhere, lor ex*
S ample, have we found references to a population of asbestos workers,
although several authors who have quoted the observed incidence of
lung cancer in autopsies of persons who also had asbcstosis imply
that this incidence applies to asbestos workers. We have likewise
been unable to find any study wfajch actually calculated the incidence
of lung cancer among a population of persons who had asbestosis, and
not just those who came to autopsy. With the exception of a paper by Doll (63), none of those reviewed gave any data on exposure and dust
concentrations, and even Doll's paper merely mentions "scheduled"
areas, by which is meant, "those areas where processes are carried
on which were scheduled under the Asbestos Industry Regulations of
1931 as being dusty."
There is, furthermore, a complete laek of definition of
l
terms as used in the published literature. Fot example, the term
0137
/
o.
asbesiosis", as usee, may refer to changes observes.* or-y by microscopic examination of the lung tissue, or it may mean a radilogically detectable condition.
Most of the published reports obviously included women among their cases, but seme of them do net give the number or pro* portion of women involved in the study.
There is also a lack of uniformity as to what type of ex* posure most studies have dealt with. Of 99 cases enumerated by Hueptr ^ ^ in 1955, only ten appear to have originated in the United
States, and seven in Canada. Some of the earlier reports apparently included asbestos miners, but it can be assumed, since 82 of the 99 cases bad originated m England, and since no asbestos muting opera* uons are carried on in that country, that most of the reported cases have involved workers in the textile or fabricating industries.
Such factors as smoking habits, family history of canesr, length of time in the industry, and age of the individual case are also notably absent tn the majority of these reports.
With this understanding of the limitations of tbs existing literature with respect to epidemiological generalisation, it may be of valuk- to consider m somewhat more detail some representative earlier publication*, a few of which were referred to briefly in the previous section.
0138
On* of (tie most oeta.leo studies and one which deserves
(ij)
tbe most ser:ous consideration is that reported by Doll
in 1955.
This study reviews esuses of destb among asbestos workers based
on coroners' records. It also attempts to estimate the risk by study
ing records of mca who worked for at least 20 years in exposed situ**
tions. Doll concluded that lung cancer was a specific industrial hazard
of certain asbestos workers and that, after 20 years of exposure, the
risk is ten times as great as for the general population.
This article is important for several reasons* in addition
to the definite conclusions at which it arrives. For example, it begins
by stating that "in view of the infrequency of asbestosis, this large num*
bar of cases (bl cases of lung cancer) suggests--bui does not prove --
that lung cancer is an occupational hazard of asbestos workers."
Neither this article or any previous one which we have examined presents
aay figures to prove that asbestosis is an infrequent occurrence. s>
timatet of the number of persons potentially exposed to asbestos dust
in the United States alone vary from 10,000 to 35,000 and the incidence
of asbestosis of any degree might be higher than Doll imagines.
This study, tike so many others, involves autopsy records,
the number of persons involved m the statistical analysis is only 113
representing only 1,042. 25 man years of life. It is also true that in
electing men whs had been employed for at least 20 years, the study
automatically excluded these who died from other causes after shorter
employment.
f\4 (
fcj-*.'.
1: a,so scerr.s that this r#v,e* dec* net ace any new cases
10 the literature, Although Hucpcr in enumerating 99 case* reported
prior to 195$, lists 11 discussed in it. Clearly, Also, the paper is
oat dealing with asbestos miners.
Another reason why this publication is of importance is
4 statement which it contains to the effect that "the stroagest evidence
( that it (lung cancer) may be a hasard (in asbestos workers) has been produced by Msrewether and by Gloyne." An examination of these
reference* leaves at least some question as to the strength of the evi
dence produced,
-
{92)
In 1951 Cloyae
presented a review of 1205 autopsies
on persons *s8 had worked in various dusty occupations. This num
ber included 152 asbestos workers, of whom 121 showed `'pneumoconiosis"
--presumably asbestosis. Primary cancer of the lung occurred 1?
times in this group, an incidence rate of 14.17* for lung cancer among
jut posted asbestosis eases. There were in his series ?96 eases with
silicosis, and b97 of these also showed primary cancer of the lung.
The incidence of lung cancer in other forms of pneumoconiosis was 6.7?,
und in le'' cases which proved not to have any type of pneumoconiosis
it was g, i**. Gloyne considered "the mortality of the asbestos workers"
to be "disturbing". First of all. it is obvious that the paper does not
(
deal wits the "mortality of asbestos workers", and secondly, it must
bv born m mine that all of Dr. Gloyne't cases wr submitted to him
0140
9.
;..r study because the iir.cing# were unusual {or uncomplicated pneumo*
.
Presumably, ail cases, including those of asbestos;*. m
m*
*huh the findings were net considered unusual were never brought to
Ur. Cloyne's attention. As 4 matter of feet, in the seme paragraph
tu which be expresses eoneern over the incidence rate m asbestosis,
Ur. Gloyne himself points out that the rote for lung cancer based on
t>*eropsies 4t the London Chest Hospital wu 21.3% while the figures
wf the ftegistrar-General showed only 2.4%. He thus reeegnised tbst
jwtepsivs on 4 certain selected group of esses were not representstive
4 the gencrsl populstion. It would seem, then, thst notwithstanding
(tu- value of Dr. Clone's work, us importance as an index of the prt*
vjence of lung cancer in asbestoties has been misinterpreted by those
*ho have quoted him. All that it really shows is the fact that in a group
.. .1. rases, selected for special study primarily because they seemed
,;.*.;rmal by preliminary examination, 1?, or 14.1% had lung cancer.
Merewethcr
in 104?, in the report of the Chief In*
ipcctor et factories, reviewed all cases reported between 1924 and
i<4b in which asbestosis was the cause of death or a coexisting con*
dttion. This work was later extended to include all such eases reported
up ta December, 19h4, by which time there were 344 deaths including
1/5 males aoc 1 3 * females. Among them were $5 cases (16%) of cancer
ot the lung, 41 in mates and 14 in females. It vs quite possible that a
large number of asbestoties who did not die of their asbestosis, or m
0141
10.
whose desth (*rti/jc[ it was net mentioned, may have been missed. The import o: this I6f is enhanced by the simultaneous statement that the incidence of lung cancer m autopsies el the general popu lation is only If*. The danger of attempting to compare a rate found in $44 eases with the rate lor the general population without respect to age, occupation, and many other variables, such as smoking habits, is obvious.
Lynch,*1*** who with Smith ***** had reported the first
case in 1935, reported four cases of eareinoma of the lung in a scries of 49 autopsies on workers in an asbestos manufacturing plant who were shown to have "demonstrable deposits of asbestos in the lungs." This, of course, is not necessarily identical with the disease asbestosis. Lynch, himself, points out that, although this is an incidence of a.2f., "both figures are too small for very serious statistical types of calculation. " Nevertheless, later writers have used this paper to strengthen the case for an association of carcinoma of the lung with asbestosis. It is of interest to note that Klotx ***** found only four in
stances of lung career in 47$ cases of asbestosis, a series 11 times as iarge. Behrens, as quoted m Merewcthcr **#1, estimated that, of 30'? eases of asbestosis in the literature, 44 showed associated cancer of the lung--giving an meioence of 14,2T*. This is another case ef generalising an incidence obtained in a group of cases which were
0142
{
11.
undoubtedly reportee only became some of them showed lung cancer,
to posttbly hundreos of asbestotics whose eases were never reported.
The same applies to the conclusion of Teleky
who appears to
have reviewed reports of J9 autopsies on persons with asbestosit among
which six eases of lung cancer occurred. Information from those sources
dees not justify generalisations with regard to mortality rates.
Werbcr *
who made the unequivocal statement that lung
(
cancer would result in from 7% to 17% of cases of asbestosis. allowed
himself considerable latitude by qualifying it. as regards time, to an
interval of
years. Finally, mention should he made of some
entirely unsupported statements which tend to build up a mistaken view
point through mere repetition. One example is a sentence in "Nemuber-
(76)
culous Diseases of the Chest"
where the authors say simply, "an ex
cessive incidence of pulmonary cancer has occurred among workers in
other occupations, such as asbestos industries, nickel-copper refineries,
stokers in generator plants, eic." without substantiating reference.
As an illustration of the ease with which a few reports which
merely suggest a certain concluaion can. through the laek of a sufficiently
critical attitude, be summarised to produce the conclusion in a definite
<69}
form, an editorial
m the Journal of the American Medical Association
mentions the work of Wedler and the report of Merewether and then es
tablishes the causal relation betwcn asbestosis and cancer of the lung as
{ settled. As a final convincing argument, it refers to "recent experimental 0143
/
u.
observation* (by) Norcir.ana and Sorge U6i}.. ^
xi t9 exaerimer.t
iA which squamous carcinoma w) iud to have been produce in about a dozen white mice, and which has set beta duplicated by any other in vestigator!
Perhaps ao one has written so extensively or so dogmata-
(109-U41
cally on the subject as has Hueper
. 2a 1955 he reviewed the
cases ***** reported prior to that date and enumerated a total of 99.
Eleven of these were those discussed by Doll (63) and appear to have
been cates covered by other authors. ight were discovered by Kennaway and Kennaway * *** in an analysis of death certificates and, unless
Merewether's study was incomplete, these eases should have been in* eluded in his report. Of the remaining SO, it ie quite poesiile that the 31 contributed by Merewetbcr and the 17 by Gloyae contain some dupli cation with eaeh other or with other Cnglish authors.
In the same paper, Hueper dismisses the idea of determining the frequency of pulmonary cancer among tbo total worker population of the aebestos industry on the grounds that it is immaterial bow many workers in the industry deviop lung cancer, since some of them have no exposure and therefore do not develop asbestostsl
0145
/
n.
UJ. PRINCIPLES OF THE EPIDEM 10LOGICAL METHOD
As ass beta indicated, much of what is now thought to be pertinent concerning the comparative frequency of lung cancer ia different population groups has been developed from the analysis of clinical material, particularly surgical and autopsy records. This has been supplemented to some extent by the reported impressions of venous clinicians based upon their personal observations. More re> ceatly, however, attention has turned to the systematic investigation ef this problem by the same methods that have proved so successful previously m the study of communicable diseases, that is to say, by epidemiological methods.
pidem>elogy is the method of investigating a specific disease in human populations in relation to certain variable character* utics, including the environment. In eontrast to the clinical method which is primarily concerned with the characteristics of the disease is individuals, epidemiological research involves the investigstion of the disease as a mass phenomenon. It seeks to discover what proper* hen of persons in a given set of circumstances will eventually develop the disease. Epidemiology cannot predict whether a given individual will fall victim to a specific disease, but it can predict the approxi* mate oumber of cases of this disease whieb will develop in a population **f specified size, composition, aod subject to a given environment. It
0145
w.
proceeds bv first carefully and Accurately describing character* istie* of the disease m different population group* and essential objective is the {emulation, testing, and verification of generali sations concerning the disease in question.
In order to apply this method of investigation to the pro* blem under discussion, the Foundation was of the opinion that a study should he planned so as to provide:
1. A well defined population group. 2. Available data for all members of this pop
ulation, including the healthy as welLas.tbe ill. 3. A sample which is truly representative of the
population. 4. Reliable and valid observations relating to the
problem of the study. A serious defect, common to most of the studies which have been reported, is that little or no information concerning the healthy people in the group seems to have been available to the author. Therefore, results of these studies eannot properly be generalised to include such people, in order to draw a generalisation regarding all asbestos workers,it is necessary for a study to include living persons as well as the dead. Limiting the investigation to autonsied cases, as bas been frequently cone in earlier studies, still further restricts its use
0146
(
m generalisation. The problem with which the C-cscz Ajsttci
MminfAssoeiation is concerned is whether asbestos miners ex*
pcricnce more lung cancer than docs the general population. The
enswer necessitates the eoUection of reliable information on asbestos
miners as a group, as well as on Che general population.
It seems advisable to discuss the differences between the
epidemiological approach and that used in the studies which have been
(
reported to date. A very important consideration is the fact that lung
cancer, in spite of its increasing numbers, is still a disease of low
incidence; that is. in a given population not many persons will contract
this particular disease. Tbis fact requires that large samples or groups
must ee stuoicd to proviee meaningful results.
Recognising the difficulty of obtaining such large camples,
most earlier writers deviated from the epidemiological method and
sought to circumvent the requirement of observing well persone by*.
1. Comparing the relative frequency of cancer
**
in various sues. Z. Comparing the relative frequency of cancer
in a group of hospitalised patients.
3. Comparing the relative frequency of cancer
in a group of caste coming to autopsy.
c The frequency of cancer of the lung relative to the total of alt typ*s oi cancer may be increased merely by reason of a decrease 0147
in the incidence of cancer 0/ other sites. Tat* could be true even though the incicer.ce of lung cancer remained constant, or u it de creased less rapidly than that of the other types.
Attemptiog to compare two population groups, looking only at the. relative frequency of cancer in various body sites, may result tn'finding a higher percentage (relative frequency) in one of the groups, when, in fact, the mortaUtv_rat of cancer of a particular organ is ex actly the same m both groups. This is bocauso the relative frequency of canetr in other organs may be lower in the second group. The mor tality rate from a particular cause is the true measure of comparison.
It is apparent that selected groups sueb as hospitalised patient* or autopsy cases may not bo representative m any way of a larger group, and that in dealing with such samples, the observer may easily find more cases of any kind than would be found in a group of the same sise, but representative of the general population. It is true that investigation of cases from sueh a sample can furniah information valu able for research, but the use of this information in drawing generalisa tions is necessarily restricted. It is the obligation of both the investi gator and of those who read hie report to make proper comparisons and to draw only thot conclusions which are valid and justified., A good statistical study o cases of cancer of the lung occurring tn a group of autopsies can lead to a proper inference concerning the frequency 01 lung cancer among cases coming to autopsy, but only to sueh cases. Tor
0146
(
p.
information i'rom such * study to b* projected to seme larger {roue,
it ;* necessary thAt the Autopsies represent a geee simple of the:
Urgcr group. To Assume thAt such is the esse in Any psrueulir series
is dAngerou* end likely to be (else.
There is some dinger the: the figures reported by some
Authors miy be misconstrued as Applying to Asbestos workers or even
Asbestos miners, when, m feet, the Authors in question do net mike
(
this generAlixAtion. nor esn the gcncrilixition be mAde for the ressons
stAted. Close study of the reports revesis thAt the percentiges quoted
rclste only to the group of Autopsies covered by the^Articuier iavestigs*
tion.
The present study, in centrist to the earlier works, his been
plinned to utilise the epidemiologicsl method. A well-defined group of
Asbestos miners hss been estAblished m such a way thAt it constitutes A
good simple of the whole popuJstion of Asbestos miners m Quebec. Diti
for ill members of this group hive been colleeteo And inilyxed. Those
concerning lung center hive received most cireful considerxtion. De-
tiils of the methods employed will be set forth in a liter section, but the
type of ipproich is considered to permit of fiir comptnsont And vilid
generiUsitions.
(
0149
16.
IV. COLLECTION a.N2 ANALYSIS Of DATA
A preliminary survey ef potential sources ol information February of l?$6 involved discussions with the physicians in charge ui the asbestos companies' prog;amt and with clinicians, pathologists, representatives ot* City and Provincial health departments and of the Canadian Cancer Society, and other interested persons. It was iwund that morbidity data, although somewhat limited, were available Iren such sources as the hospitals in Montreal and Quebec City, and the U Cancer Detection Centers in the Province, However, because 01 the high mortality in lung cancer, it seemed advisable to depend upon 1-u relating to deaths. These we found te be obtainable at the vital fuusttcs department of the Ministry of Health in Quebec City. From the preliminary survey, it was apparent that extensive and detailed in. formation could be gathered with respect to both the persons employed m the asbestos mining industry and mortality figures for the general population.
Following this exploratory survey, the initial effort was directed to the collection or' data relating to all workers who had been .ro<i-seo tnrougr. the clinic at Thetford Mines since its inception in l'H*. Similar information was obtained regaromg all workers at the Canadian Johns.ManviUe Company m Asbestos. Data from the clinical records included the age, family and personal medical histories, smoking habits, number of years of exposure, an estimate of weighted exposure.
015
and the course of the individual's health status or the cause si his death. Although the data is these two instances were not exactly similar in form, the inclusion of records from the personnel deportment At Asbestes covering employees who hod retired, died or become disebled provided dou sufficiently Alike for the purpose of the study.
From this information it was possible to formulate for both Asbestos And Tbetferd Mines "cohorts" which could he well defined, Should be representAtive of tAeh group, And could be followed for a de finite period of time. All of the Aveileble experience indieetes that the development of Asbestosis in less then five ycers of exposure must be somewhat rare. Accordingly, the cohorts were defined as including every worker who bad a total exposure of five or more years, and who was oe the employment rolls at Asbestos or Tbetferd Mines in 1950. These cohorts were then followed by means of the annual physical ex amination records through a six-year interval, 1950 through 195$. All data regarding these groups were then tabulated m order to determine the characteristics of the cohorts. For those who survived the entire period, reference was made to the physical examination results and xray findings at the end of the period. Those who had died were tabulated separately and the cause of death corroborated by examination of the death certificates. A further eearch was made concerning those in the original cohorts who remained unatcounted for when the living and the known dead had been tabulated. They represent men who had left
table :
Number of Person* and Number of Lung Cancer Deaths by Length of Employment
Length
Asbestos
Thetferd Mines
o!
Lur.,;
Lung Cancer
Employ-
Cancer
Deat hs
men: Person* Deaths Persons Proves Tot*;
Combined Lung Cancer Deaths
Persons Provee To:*;
5-9
880
0
915
0
0
1795
0
0
10-19
864
0
1534
1
1
2398
1
1
20-2*
142
1
SBC
2
2
922
3
3
*0-34
168
2
435
3
5
603
5
7
40-44
17
0
168
0
l
185
0
1
2
0
53
0
0
55; 0
0
Tot*l
7m
T Tool
6
9
5937
9
TI
Jo
4
Annual Lung Cancer Death Kates per 10C.OCC Man-Years oi Exposure by Length of Employment
Length of Employment
5-9 10-19 20*24 30-39 40-49 50* Over-all
Asbestos Total
0 0 49 196 0 0 22
Thetford Mines Proves Total
0
0
11
11
57
57
115
192
0
99
0
0
27
41
Combined Prove Tota.
0
0
7
7
54
54
138
193
0
40
0
0
25
34
0170
Number of Persons and Number of Lur.g Cancer Deaths by Exposure Category
Expos. ure
Cate. ^^orv^
Asbestos
Thetford Mines
Combines
Lung Cancer
Lung Canter
Cancer
Deaths
Deaths
Persons Deaths Person* Proved Total Persons Proves Total
I
964
2
1062
2
2
2031
4
4
II
564
1
1586
2
3
2150
3
4
111
?as
0
1037
2
4
1772
2
4
Vnknowe
5
0
0
0
0
5
0
0
Total 1273
3
3665
6
9
5456
9
u
Annua) Lung Cancer Death Rates per 100,000 Man-Years of Exposure by Exposure Category
Exposure Catecor
Asbestos Total
1
34
11
30
m
0
Uotaown
0
Over.all
22
* No one exposed
T'netford Mines Proved Total
31
31
21
32
32
64
0
27
41
Comb: Proves Tata.
33
33
23
31
19
37
0
0
25
34
0171
40.
j exposure i asbestos ;* i?. any way connected to lung cancer, w would expect that the longer and heavier the exposure, the higher the rste that would be found. The only possible error la this interprets* non could occur 11 the weighted exposures were inversely reined to peers of employment, in which cese the heaviest weighted exposure (category XU) would show the shortest length of employment. Tables 9, 10, and 11 which list the number of persons in various exposure categories by length of employment indicate that this error has not occurred. In fact, the average number of years of employment for each exposure category is almost identical.
TABLe 9
Number of Persons m Various Weighted Exposure Categories by length of employment
Asbestos
Length of c:o.ov?r.r.t
$-9 10-19 0.29 5040-4*0 * Teul Av. Yrs. of Lipcsure
Wetcbted exoeswre Catetenet
l
U
in
428 2?> 159
98 9 2
469
15.5
212 21?
89 42
3 0 $04 15.2
239 3?3
92 27
4 0 73$ H.5
Unknown
0 l 2 1 1 0 ' 5 29.0
Total
880 864 342 168
17 2
2273 15.1
0172
/
4;.
"ABLE iO
Number of Persons in Vartous Weighted Exposure Categories by Length i Employment
Thetford Mines
'Length of Employment
$9 JO-19 20-29 30-39 40-49 50 Total Av. Yrs. of Exposure
W)(hted Exposure Categories
1
U
m
279 390 155 149
67 22 1092 19.9
385 666 2?4 176
64 21 1566 18.7
251 478 1S1 110
37 10 1037 18.1
Unknown
0 0 0 0 0 0 -'0
Total
915 1534 580 435
166 53
3665 18.9
TABLE 11
Number of Persons in Various Weighted Exposure Categories by Length of Employment
Combined Asbestos and Thetford Mines
Length of Emoloyment
5*9 10*19 20.29 30-39 40-49 50 * Total Av. Yrs. of Exposure
Weithttd Exposure Categories
1
Ji
m
707 663 314 247
76 24 2031 17.8
598 633 363 213
67 21 2150 17.6
490 851 243 137
41 10 1772 16.6
Unknown
0 1 2 I 1 0 5 29.0
Total
1795 *2398
922 603 185
55 5958 17.5
C17
\ I
J
t
Table 12, which develop* the rates for smokers and r.on-
smokers, is most striking. It shows that not a single case of lung
!
cancer developed among the 1265 nonsmokers and that all cases of
i
i
lung cancer, both "proved" and "suspected'', occurred ux smokers.
A comparison of Tables 8 and 12 certainly suggests that smoking is
a greater baaard than exposure to asbestos in tbc mining operations.
1
Table 12 was so striking that it was felt that further veri
i
i
fication was accessary. It was possible that some abnormal distn-
\
i
bution may have occurred, e.g., the nonsmokers may have included
i
| a larger percentage of young men. Consequently, additional Tables. 13, 14, and 15 were constructed to bow the distribution of smokers
i
and nonsmokers by age, length of employment, and degree of exposure.
Although there are slight differences, they do not account for the laet
that all observed eases of lung cancer were in smokers. In respect to
sgc (Tabic 131 the combined average age of the smokers was 4.9 years
less than that of tbc nonsmokers. Table 14 shows that as far as length
of employment is concerned, the smokers had worked about 2. 3 years
less on the average than tbe nonsmokers. With longer exposure end
greater age, otic would expect the nonsmoking group to show a higher
rate if lung cancer were due to asbestos.
Table 15 shows that the average exposure category was al
most the same for tbe two groups. Therefore, thus variable seems to
be of no importance in accounting for the difference between lung cancer
death rates for smokers and nonsmokers.
0174
43
TABLE 22
Number of Person* end Number of Lung Cancer Deaths by Smoking Habit*
^Tbetford Mines
Combined
Lung
" Lung Cancer
Lung Cancer
Cancer
Deaths
Deaths
Persons Deaths Persons Proved Total Persons Proved Total
Smokers
1951
i
Nonsmoker* 540
0
UiUaowa
2
0
Total
TZtj
1
2742
6
925
0
IS
0
5685
?
4
4675
9
12
0
1265
0
0
0 . 20
0
0
5956
9
12
Annual Lung Caneer Death Aates per 100,000 Man.Years oi xposure by Smoking Kabi:*
Smokers Noasmokers Unknown Over .*11
Asbestos Total
26 Q 0
TT
Thctford Mines Proved Total
56
55
0
Q
0
0
T7
41
Combined Provee Tota
32
43
0
0
0
0
25
34
0175
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0178
V-
4-.
The result of this additional analysis t* that none oC these factor* appear to lessen the effect of Table 12, which ;* therefore tron|ly suggestive of the importance of smoking as compared to the other variables.
Asbestosis and Lung Cancer
When we attempt to relate the lung cancer deaths occurring
in the cohort with the reported cases of asbestosis, we are immediately
aware of a disturbing inconsistency. Various authors report the incidence of asbestosis after 10 or IS years of exposure as exceeding $0%, and ;r.
one study, as high as 8?%,
However, data on
caacs of asbestosis from the cohorts at Tbetfsrd Mines and Asbestos pro*
dues a rate of only about $%. It is true that these data are based on only those cases whieb have bees proved at autopsy, and those whose most :
cent xray interpretation resulted in a diagnosis of asbestosis. This in
cidence may be far lower than if based on microscopic examination of the Jung tissue. As a matter of fact. Dr. Cartier has estimated that there are
probably 300 workers who do not shew radiological evidence of asbestosis,
but who have some degree of fibrosis. He also estimates that there are perhaps 40 workers wbu may have died or retired with this disease. Instead
of 143 cases of asbestosis m the whole working force at Thetford Mines,
w should then have perhaps $00, but even this would result in an over-all rate of less than 10?, which is far below those widely reported, in our
0179
combined conort, there are 1765 men who have had mere than 2 years.0/ employment, and 431 of these have worked in the heavies: avera(t exposure. Accordant to the records, we can account /or only 13d cases o asbestosis ia tbc combined cohorts. If even o/ tbc workers with more than 20 years1 exposure develop asbestosis. we should expect about 423 cases. This leads us to believe that there is a very considerable underreporting of asbestosis. Such a hypothe* sis is easily conceivable when one considers that many chest x-rays in this group may be considered normal by comparison with others
\
isv the same group whereas, if they were to be compared with wba: are considered as normal cbest x*rays elsewhere, they may be inter, preted as showing fibrosis.
Cases of asbestosis which were accumulated from the au. topsy records and from the periodical physical examinations result m a distribution wbieb is shown in Table 16.
TABLE 16 Distribution of Recorded Asbestosis Cases
In Cohort
Living Deao
Total
Asbestos
16 4
22
THct/ord
66 30 116
Combined
104 34
136
TABL 17 - Pa.-:
Nussbcr of Asbestos:* Cases By l.er.gti of ajpioyHent And xpo#ure Category
Asbestos
i>b of Zmolovraeat
Less tbAO 10 10.14 20.24 50-14 40.44 50 TotAl
Av. Trs. of Employment
Closure Cateeorv
111
0
0
0
0
1
2
2
7
4
0
1
4
0
0
1
0
0
0
2
9
11
25
25
29
Unjciow-
0 0 0 0 0 _0_ 0
TotAl
0 5 11 5 1 0 22 27
Pereeatage* of Asbestos:* Cases By Leagts of Sspioymoat and Exposure Categ'try
Lcagtb of Emolovwen*.
Exaosur* Cates orv
1
u
111
Loss than 10 10-19 20-29 50-59 40-4 50 Over.*11
0
0
0
0
.5
.5
1.3
7.9
4.3
0
2.4
14. S
0
0
25.0
0
.2
1.6
1.5
* No one exposes la :b:s gro-p
Unknown
a 0 0 0 0 0
Total
0 .3
3.6 3.0 5.4 0 1.0
0181
so.
7A3L :? . Pi-t u
Number of Asbcstost* Cue* By Length of employment and exposure Category
Tbetforc Stines
Length of molovment
Loss than 10 10^19 20-29 30-39 40-49
.50 Total Av. Yrs. ol employment
xnosure Catetorv III
0
0
0
0
1
7
2
5
21
2
15
33
0
6
20
0
2
2
4
29
3
30
36
34
UnJoowr.
0 0 0 0 0 0 o
Total
0 8 2$ 50 26 4 U6 34
Percentage* of Asbestos:* Cases B'i* Lor.gth of mp;eyrsisat one exposure Ca:.egory
Length of Cmelovmer.t
Lnoturt Co: ecorv
4
U
111
Unknown Total
.it'-
Loss (boa 10
0
0
0
o
10-19
0
.2
1.5
0
.5
20-29
1.3
1.8
13.9
0
4.8
30-39
1.3
8.5
30.0
0
11.5
40-49
0
9.4
54.1
0
15.5
50
0
9.5
20.0
7.6
OvT-*ll
.4
1.8
8.0
0
3.1
* No one exposed in this group
0182
51.
TABLE 17- Pert IE
Number of Asbestosis Cases By Length 0/ Employment and Exposure Category
Asbestos tad Tbetford Mine* Combined
Length of Emoiovmer.t
Lea* then IQ JO-1? 20-2? 30-39 40-49 30 * Toul
Av. Trs. of Employment
Exposure Ctteeorv
n
. ill
0
0
0
0
2
9
4
12
23
2
16
37
0
6
21
0
2
2
6
36
94
2$
33
33
Unknown Total
0
0 0 0 0 0
T ?
0 11 41 35 27 4 138 33
Percentages of Asbestos!* Cases By Length of Employment sne Exposure Category
Length of Emelovmer.t
Exoosure Carecorv
I
U
ill
Less than 10 10-19 20-29 30-39 40-4 SO * Over-all
0
0
0
0
.2
1.0
1.3
3.3
10.3
.8
7.3
27.0
0
9.0
$1.2
0
0.5
20.0
.3
1.8
5.3
* No on* exposed in this group
UnJctown
* 0 0 0 0 0
Total
0 .5
4.4 9. 1 14.6 7. 3 2.0
0183
a.
A percentage mctder.ee of asbestosts :'or ecn exposure ca:cgeryshas iti cevelepec a* well as ier each per:c o: employ ment. This information is shown is Table 1?.
It will be noted that wubin an exposure category, the incidence rises with increased length of employment. It is also apparent that the incidences, even in the category 0/ heaviest ex
r posure, are far below the rates found by the authors preyiousiy re ferred to. It seems clear, that unless concentrations of asbestos dust to which the miners are exposed are very much lower than those which ootaia in all the other stuetes, there has been across under reporting of the asbestosts eases. The obvious result is a higher relative frequency of lung cancer in association with asbestesis. Table 19 compares deaths due to lung cancer and fatal cases with abestosis, alone and ift combination with eaeh other.
TABLE IS - Part I Statistical Analysis of the Causes of Besth
Asbestos
Cause
Atbestosls No Asbestosts Total Pttter.tite
Lung Cancer
M .2)
21 2.6)
3
5.1
No Lung Cancer
.3 0.3)
43(42.3)
ii
43.9
Total
"4
45
49
Percentage
1.2
91.9
Figures in parenthesis are the "expected" numbers
0184
\ V-
* .r* '
$3.
TABL 18 . P*r:r Statistical Analysis ex the Causes ex' Death
Tbetford Mine*
Cause
Asbestos;* No Asbestos;* Total Pereeotaee
Lung Cancer
3( l.))
3 ( 4.7)
8
Ho Lung Cancer
iitfb.n
101(99.3)
128
Total
28
TO-
132
Percentage
21.2
78.8
4.5
n.s
figures in parenthesis are the "'expected" numbers
( TABL 18 Part SI Statistical Analysis of the Causes of Death Asbestos and Tnetford Mines Combined
Cause
Asbestosis He Asbestos:* Total Percer.tate
Long Cancer Ho Lung Cancer
Total Percentage
4 ( 1.8) 28(30.4)
32 17.7
S( 7.4) 144(141.8) 149 82.3
9 172 U1
5.0 95.0
Figures in psrenthc sis are the "'expected" numbers
Sin deaths from unknown causes not included
The number of lung cancer deaths combined with asbcsiosi*
is larger than would be expected in caeb cohort and in the combined
cohort*. Thi$ diilercr.ee is significant at the 9$% level using the ehi-
square test oi significance. The importance of the under-reporting of asbestos;* can be observed in Table 19.
0165
5-t.
TAB LX P
Statistical Analysis e:' th Causes of Death 20 Nonssbestosts Cato baa beta Diagnosed aa Aibtitoiu Cases
Cause
Asbestosis Ne Asbestoais Total Percentage
Lung Cancer No Lung Caacer
Total Ptrctau|c
4( 2.6} 48(49.4) 52 28.7
S( 6.4) 124(122.6) H9 71. i
9 172 181
S.O 95.0
Figures ia parenthesis are the "expected" numbers
?
la this table, it has beta assumed that 20 of the cases which did aot have lung caaeer had which were reported to have ao asbestesis did. ia (act, have asbestesis, the diagnosis o which was missed. Although the cases of Lung caacer with asbestesis are still higher than would he expected, the difference is no longer significant at the 9S level. This still is true if fewer than 20 cases were shifted hut U ts rsasonsbls to expect that at least 20 of the 144 might have shown asbestesis bad they been subieet to autopsy. On ths other head, a shift of about 40 cases would produce aa expected rate almost equal to tbe rate found. Explanation of this effect of under-reporting of as* bestosis has been stressed beesuse it seems so obvious that in under* reporting asbestesis the relationship between it and lung caacer has been made to appear more significant than it probably is.
01P6
c
t
few"
i i
Four of the proved east* of lung career -ard cee of the suspected were associated with asbestos*a. Since we have only 32 deaths in which asbestosis was present according to the records, the incidence in this series is U.$%. waile this is slightly lower thaa the rates found by Merewctber, Gloync, and Wedier, it is still such higher thaa could be expected if the asbestosis incidence were anywhere near the experience reported by other authors.
t Comparison of the Cohort xoerience with that of the
Province of Quebec, Dominion oi Canaoa, asc the United States
la order to make a comparison of the experience among asbestos miners with that of the general population oi the Province of Quebec* statistics were gathered, as stated earlier, in the office of the Division of Demography in the Provincial Ministry of Health. The data on total deaths, deaths from all forme of cancer, and deaths from cancer of the lung were obtained by sex and by county for the years 1950 through 1955. la addition, all death ccrtiiicatee which spcctfied primary cancer of the lung, and all those.which indicated lung cancer but did not specify the origin, were examined for the years 19S2 through 195$.
7able 20 gives a tabulation of the number of deans from lung cancer in the Province ana in the two cohorts for the years 1950
through 1955, and shows the annual rate per 100,000 in these segments. 0187
5b.
It will be notec from the (Able that the mortality rate for the Asbestos eobort : finest exactly the same as tbit lor the Province, while tae rote for "prove*" cascs m the Thetford Mines cohort is only slightly higher. When the "suspected" cases Are included is the calculation, the rotes for the Tbetford Mines co'hort rices to 41.4 per 100, 000 which is Marly twice as high as the rate for the Province. This, it will be recalled from the previous discussion of the "suspected" cases, ap proaches but does not exessd the signiiicanx level.
One further interesting observation from Vablc 20 is the rathtr marked increase in the total number of cases for the Provmce between 1 ?50 and 1955. It is assumed that at least part of this increase is due to improved recognition and reporting of lung cancer during the interval. For this rsason, the years 1954 and 1955 were thought to be more nearly representative of actual conditions. vsn so, it is quite likely that the general population is sot studied for lung cancer with the samr diligence wuh which this disease is looked for in the miners, and it seems probable that tbs mortality rate's for the Province would tend to he low. This would appear to be substantiated by the fact that the reporting oi cases in the combined cohort showed no such increase over the same period.
Table 21 was compiled to show the annual age-specific lung cancer rate of cases in which the death certificate merely read "cancer of the lung", as distinguished from those in which the diagnosis was
01SS
A
alive In cohort at beginning ol 19*2.
c
k:.
e
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57.
e
AN S
e>
s
9
*
5 V
A %
<fc*
* w So- 2e -- (I ,, e 3 ..2e *
~ O : E
<
0189
56.
confirmed by autopsy, surgery, or biopsy. The terns 'specifies
primary1' refers to those coses is these torse two categories m
which the tumor *t specified as havisg originated is the lung. It *Ui be noted that, ol the toul coset certified is 115$, o much higher
pereestoge thoo is 1954 was specified os primary. The table olio
shows thst s higher pereestoge of the toul coses certified is 1955
were proved, again indicating isereosisg isterest is this diseose.
A coxsporises hot bees mode between the age-tpeeifie rotes shows is Table 21, osd those for the cohort shgwn is Table 6.
As overage of the 1954 osd 1955 rotes for the Frovutee hos bees used,
since the 195$ figure woi higher osd may hove bees exceptional.
This comparison, summarised is Table 12, shows that the
observed number of deaths is our sample is sot signifieastly greater
than the expeeteo number of deaths, based os the average of the 1954
and 1955 figures for the Province. It is true that, is the esse of the
age group of 65 osd over, the five deaths provide a figure whieh is al
most significant at the 95? level. However, it ehould be noted that
this number includes one of the euspeeted but unproved cases previously
referred to. furthermore, it is rather likely that the rate for the gen
eral population is usderstated is this age group, for the obvious reason that tbc exact cause of death in tbc very old is not a matter of the same intensity oi interest as it is is younger persons.
0190
f i
\
A
A
59.
Before leaving this comparison of the Province with the it should be shown that their age distribution* sre reasonably the lime. That this is the esse can be observed from the following tabulation;
Age Distribution of Adult Males for the Province of Quebec, 1951 (Support, 1954)
Are Crous
Number
20*44 45*54 55*64 65 Total
727,135 186.952 128,944 113,46? - 1,156,496
Percentage
63 16 li 10 100
Percentage Combined Cohorts
r -
66
19
10
5
100
lt should be remembered tbit the miners retire sac con* sequeatly, it eon be expeeted tbit the oldest oge group will be Urger is tbe general populition. The dots presented in Table 25 indicstes that tbe lung eoncer rite generally deercises ifter ige 70, ond we could expect tbe rote for ill people over 65 would be smeller thin the rote for i group of 65 to 75, which would apply to the oldest group of miners. It is felt that by using the whole adult male population, wc have developed rates which are somewhat lower than if we bad been able to exclude the general population over 75.
( 0191
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b 0 > --
9
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0192
TABLE 22
Comparison of the Actual and Expected Number of Lung Cancer Deaths by Age Among Asbestos Miner*
Age Grouo
Province Total Specified Primary
Bate oer 100, 000
No. of Miner*
Expeeted* No. of Deaths
Observed So. of Death*
Proved Total
20-44 45-54 55*64 65 4 Unknown
1.9 24.5 67.6 9.3
--
3931
0*
1124
2
615
2
315
2
3
--
1
1
1
3
3
3
4
5
0
0
* Actually .4 f
4 The expected number is baaed or. tbe eve rage of tbe 1954 and 1955 age*apcettic rates for tbe Province of Cuebec.
Table 22 Mao answers a question previously raiaed. It
a how a that the secttri of theae cohorts have not died from lung can*
car at as age earlier than the general population, and that sucb an ex*
M
pianatiee cannot be ottered lor the abaence of lung cancer in 240 men with more than 40 ycara of employment referred to on page 3?.
A companion between the aabcitoa miner a and the popu
lation of the Dominion aa a whole via made, uaing statiatical material
from several source*, in one source, Phillip*
gave age* End aex*
specific rates for Canada for three periods between 1931 and 1952.
The rates for males are given m Table 23.
c
0193
6 2.
r*\
TABL.C 23
Annual Death Rate* per 100,000 for Cancer of the Lung an Canada*
Age Croups
Unde? 30 30*34 35-39 40*44 45*49 50*54 55*59 60-64 65*49 70-74 7**79 80*64 85
All Ages
1931*1933
0.2 0.9 2.0 3.0 5.2 8.2 12.7 12.5 15. 1 10.7 15. 8 8.2 11.4 2.8
Crouos of Years I941*r43
0.3 0.9 3.2 S.4 22.5 18.9 27.0 33.7 34.5 30.6 30.0 27.9 14.3 7.1
195Q-'.C52
1.0 0.8 3.0 6.5 16.7 37.2 59.7 77.8 102.9 86.3 13.9 59.7 71.0 15.8
"Mortality from Lung Cane er in Canada", 1931 to 1952.
These figure* shew strikingly tie increase in rates be*
tweea 1931 and i952. and this increase is particularly marked after
age $0, confirming an observation previously made, to the effect that
lung cancer has probably been under-diagnosed in the older age groups
in the general population.
To use these figures for purposes of comparison, it is
necessary to combine the rates for certain age group* in order to
c
conform to the age distributions used in this study. Since the exact
populations m eaeb age group for the years indicated is not known.
0134
/
\
63.
this must be aa approximation. However, tbe rotes would be some* what os follows:
Ace Crouo
20.44 45*54 55.64 65 v
Rat^
5 2? 69 90.95
These rotes ore, is general, lower this those developed for the total (proved and suspected) eases of lung caster among the asbestos misers. The only large difference, however, is in the age group of 65 years and ever, and it is quite possible that tbe rate for this group say have increased for Canada between 1952 and 1954 as it did for tbe Proviaee of Quebee. (Sec Table 21}
A further comparison bas been made with aa over-all rate obtained from the American Cancer Society for respiratory can* cer deaths in Canada in 1952. This rate, for males, is 20.5 per 100,000, an increase of 5 per 100,000 over Phillips' lo50*1952 rate, and compares with 25. 5 per 100,000 for proved eases and 54.0 per 100,000 for total cases among the asbestos miners in this study. It i* therefore obvious that there arc no important difference* between the rates for asbestos miners and those for tbe general population of Quebec and the Dominion of Canada.
0195
64.
Sisc it is prooafeie that figures ter the w'a;uc iuu< are more complete and, therefore, possibly more compatible to the eat* for tbe miners, age.specific rites were computed from "V;ui Statutics of tb* United Sutes-', Volumes 2 sad 12. for 1952. These rites have been tabulated m Table 24.
TABLZ 24
Number of Oeitbs lad Death Hites per 100,000
by Age Croups for the Adult Mile Population of
tbe United Sutes--Data From
.
"Vital Statistics of tbe United States", Volumes 1 Cad 12,
1952
Ae Crouo
20.44 45.54 55.64 65 a Total
-Peculation
24,544,000 1,065,000 6,340,000 5.670.000
44,619,000
Cases
883 2979 6254 6483 16,599
Hate oer 100. 0C0
3.6 36.9 98.6 114. 3 17.2
It is apparent that these rates compare favorably with those for tbe asbestos miners as shown in Table 6. Still other rates for tbe United States wre obtained from the American Cancer Society, and for males, these were 25. 3 per 100, 000 m 1953, and 28.0 per 100, 000 in 1955. They are not idenueal with tbe rate calculated from the figures of the office of Vital Statistics, but this is possibly because tbe American Cancer Society rates are tor males of all ages. Nevertheless, they, too, compare favorably with the rates of 25 (or 34 for tetaJ cases) obtain;.-.; among the asbestos miners
01S6
l. \
65.
Returning to 4 comparison hetwten the asbestos rr.;r.e.*s
-d persons who arc exposed to asbestos in one form or another (as
distinguished /rent the general population groups ;ust discussed, who
have no exposure) an interesting observation can be developed by tt-
. .
,,
(122)
suction. Hueper
has stated that there are about 35, 000 persons
exposed in the United States, and we have found that the Canadian
mines employ about 8,000. Elsewhere, it has been estimated that the
workers in England who have exposure total between 3,000 and 5, CSC.
With workers ia Africa, Denmark, Norway, and other countries, at \
least $0,000 persons must be exposed throughout the world, and it can
be assumed that this number bas been fairly constant in the 20 years
since 195$ when the first case of asbestosis with lung cancer was re*
ported. At least a million man-years of exposure has thus been accumu
lated, and this figure can be divided by the approximately 150 eases of
lung cancer with asbestosis reported during the 20-year period. This
gives a rate of 1$ per 100, 000 which is at least indicative that any lung
cancer rate which caa be calculated lor worker* exposed to asbestos
dust is not much greater than that for the unexposed persons.
0197
(
be.
Comcaricr. Sutler. S.iht Counties Aoacm ? :;
Asoe:os?rouuc.r.^ Arcus ar.~
acicctcc wO'--
To compare lung cancer mortality rate* m the coun
ties surrounding the asbestos-producing ire** with mother group
o/ counties m which no asbestos miner* ire likely to reside, the
c rites ere computed on the bisx* of figure* for the yeir* 19S0 through i*55. Toe eight counties selected for corepinson were Argenteual. Chiteiugiy, Montaagny, Pertneuf, Richiieu, Riviere-
du-Loup, St. Kyacintne, md Terrebonne, mainly because they re
present i wide geographic distribution throughout the Province. The
counties selected because of their proximity to the asbestos mines
include Artaabaik*. Seauce, Drummond, Prontenac, Megantic.
Richmond, Sherbrooke, mo Wolfe. Table 25 shows the number of
lung cancer deaths for the years 1950 through 1955 for each of these
counties, mo a mortality rate, eased on the adult male population
in 1952. To empnauxe the comparison Megantic County has been
'''**2
shown separately, as das the Province of Quebec and also the Pro
vince with the eight *soetos.precueing" counties subtracted. Be -
cause e: its unique
cancer death rate, Montreal et Isle ce Jesus
ha* also oeerv usteo m orcet to provide further comparison.
t 0198
0*99
N um ber o( U un| C ancer D eath* and Rate p e r 100,000 M a n -Y e a re
*
A Sn nA aa a
l 19
r*\
66.
It is Apparent from the table that the lung cancer Ceati rate /or the eight counties immediately surrounding the asbestos* producing areas is practically identical with that or igh; counties selected lot comparison. While Megastie County has a rate nearly twice that ol the combined eight selected counties, it is lower than the rate /or the Province, and considerably lower than tbe rate lor Montreal. Ac figure for Montreal would certainly be higher except lor the very low numbers ol deaths reported lor I960 and 1991, and it would appear that seme error in reporting has undoubtedly been made. On tbe basis ol the other years, I960 and 1951 deaths would be expected to be about 200 greater, and this would result in a rate ol eO per 100,000.
Ac only possible conclusion from this comparison is that there is no evidence that the persons who live in the counties surrounding and adjacent to the a*bestos*producing areas have any greater incidence ol lung cancer than those who live elsewhere in the Province.
Discussion ol All Recorded Lunc Cancer Cases.
Living and DciC. at
:nei ano Thciiord Mines
Although a simple enumeration el all the known or sus* pected cases ol cancer of the lung in these areas has no particular value Iroro a statistical point ol view, it is ol interest to summarise
0200
\
0.
such cases for the record. There were r.jnc death* pr;sr to the teginasg o.' the tune period covered by the study, including one is which the diagnosis ii mediastinal lymphosarcoma. Ail of these nine ease* occurred at Thetford Mines. It is somewhat surprising that there is so record ot any lung cancer deaths among the Asbestos group is the istcrval preceding the beginning of the study and equally o that so cases have bees reported in 1956 and 1957. During the period covered by this investigation, there were six proved cases and three suspected cases at Thetford Mines, as well as three proved cases at Asbestos. Through 1956 and to date in 1957, there were eight deaths at Thetford Mines, six of which were merely suspected and included such diagnoses as mediastinal lymphosarcoma, mesothe lioma, cancer of the leg with metaetases to lung, absess of lung, and
cancer of the pancreas. One other was diagnosed on the basis of x-ray only. In addition, there are now living four eases in which the diagnostic
evidence is strongly suggestive of lung cancer. This is a total of 35 cases of all type*, including tea "suspected" but unproved cases, and
four that arc still living. The remaining 19 constitute the total of proved
cases of cancer of the lung m both areas since 1940. Sixteen of these
bave been at Thetford Mines and only three at Asbestos, all of which
occurred during the period of the study.
The proved cases averaged 59 years of age at death, and
varied between 3? years and 61 years. Their working span covered
0201
70.
period* varyir.g ber*een 4 minimum 01 14 years ar.c siur^s 0i 37 y4rs. Only three men bed lees then 25 years of employment in the industry. Seven among those on whom such information is available had a weighted exposure placing them in category 112, and six worked in an exposure represented by category!.
Although they were subjected to post-mortem examination, there were three among these proved lung cancer cases in which we do net have information regarding the presence of asbestosis. Of the remaining 17. asbestosis was present m amt. although it was minimal in rwo. and rwe pathologists disagreed regarding tta presence m one. igbt of the proved lung cancers, therefore, were not accompanied by asbestosis.
0?0"
r
t
-irtO
VI. SUNLMASY AN3 CONCLUSIONS
Interest is tbc question 0/ whether there ra*y be an it> aociation berweeo lusg cancer and asbestosis or exposure to asbes* tee has beta evident since the report in 1935 by Lynch end Smith of a case is which lung caneer tad asbestosis were both pretest. As additional cAe is which the two diseases coexisted were reported, a cAtuAi AteoeiAtion appears to have bees gradually Accepted by many Author*, although a few worker* considered the correlation to be in conclusive. Cases ot lusg eeaccr which bed occurred Among the asbeeto* miner* is Quebec hod been carefully recorded over the year*, and the pretest study wa* comaieeiosed is as effort to determine whether a caueal relationship did, is fact, exist between exposure to asbestos and cascer of the lung.
Jtefercsee to the literature ehow* a remarkable uniformity both of method and of coaclueiose. In general, the method ha* bees to study a circumscribed series of cases of asbestosis and to enumerate those is which lung cancer occurred. The series may consist of eases coming to autopsy or of dtatb certificates mentioning asbestosis, and tbc total number bas served as the denominator by which the number of lung cancer cases is divided to produce s certain "incidence raw". Tfcis rate, aa reported by various autbors bas been consistently high, and Us uniformity is indicated by the following tabulation.
0203
:z.
r\
Author
Merewether W*dler Wycrs Lynch L Cannon Gloyne
Totals
Asbeetosis Deaths
344 92
1 IS 40
121 712
Cancer oi Lund
55 15 17
3 1? 107
Percentage Incidence
16.0 16.3 14.8
7.5 14. 1 15.0
At notable characteristic of all previous publications
is the adherence to the development of a percentage relationship in
' '
(63)
a relatively small and very selected group of cases. Only Doll,
among ail of these authors, has described a representative population
group and studied it for the mortality rate from lung cancer and com*
pared this rate with that for a control group. His investigation dealt
with only 113 men in the study population.
Sines most earlier studies had been limited to enumerating
the lung cancers found in certain selected samples, such as cases
coming to autopsy or death certificates in which asbeetosis was men*
tioned, it wit apparent that they could not fulfill the requirements of
an epidemiological and statistical approach to tbs problem. The pre
sent study was, therefore, designed to meet the requirements of this
method.
After a preliminary survey to explore the availability of
reliable information, data were gathered on workers in the asbestos
mines is Quebec, based on medical records at the two mam locations
020&
73.
Of these operations. Cohorts were de.'ineo according to certain cri
teria tsd &U workers who met these criteria were included in the
study. Through their medics! records. data relative to their charae-
teristics were collected and their status at the end o/ a six-year period
of observation was determined. In the case of those who had died, an
exhaustive search of death certificates aad-insurance records was
carried out is order to determine as aearly as possible the exaet cause
of death. Mortality rates from lung cancer for the general population
of the Province of Quebec and its various counties and for the Dominion
of Canada, as well as the United States were calculated from statistics
collected in the appropriate places. Comparisons of the rates obtained
for asbestos workers and for tbe other population groups were made
according to accepted statistical methods which have been explained in
some detail in section IV.
Records were obtained on 6091 persons who fulfilled the
'
criteria of our cohorts. It was not possible to trace 133 of these for *
the whole period, hut $771 of tbe remaining 5958 were found to be still
living in 1955 or later. Of the 187 toiswn dead, cancer of the lung was
considered to have been reasonably proved in nine and to be strongly
suggested in three.
The members of tbe cohorts were studied with respect to
age, length of employment, a weighted average of their exposure, and
their smoking habits. Pour thousand, six hundred and seventy.three
/
.
?4.
tr* fowna to bo smoker* -aitkin :h definition of that lerm at uscc i& tbit study. Thirty*four percent of the cohort were mote than 4$ years of age, and 30% bed been employed for longer than 20 years. Thirty percent bed a weighted exposure which pieced them in category U2.
The mortality ratee for lung cancer, a* computed on the haeie of ui "proved" deaths among the Thetford Mines cohort and three "proved" deaths among the Asbestos cohort, were 27.6 per 100,000 for the Thetford Mines group, and 22.2 per 100, 000 fox`the' Asbestos group. When the three "suspected" cases were added, the "total" rate for ibc Thetford Mines cohort rose to 41.3. The rate for the combined cohort was 2b.S per 100,000 for "proved" eases, and 34 per 100,000 for "proved" and "suspected" cases. The importance of the suspected hut unproved cases in determining these rates has been rtitersted be* cause it is likely that such cases would sot be included in the statistics for the general population.
According to tbe findings in this study, the mortality rate from lung cancer does net appear to increase with length of exposure or with degree of exposure, a fact which presents strong evidence a* gainst the carcinogenicity of asbestos. Os the other hand, the study indicates that cigarette smoking is a very important faetor m the in* cidence of cancer of the lung.
A comparison of relative frequency of lung cancer and as* hestosis ts less reassurinc. hut w believe that this is because of an .
0*06
*5.
uki. Tat
iueiui.i
indicated by tbe medical records is far below tint which would be
expected on tbe bests of ell previously published figures. Naturally,
when tbe esses of lung cancer are compared with an artificially low
figure, its relative incidence will be bigber than it should. However
this may be, 12.$% of the recorded cases of asbestesis in this study
developed lung cancer, a figure slightly lower than those quoted by
authors who confined themselves to this type of eomparisoa.
Comparison of the experience among tbe asbestos miners X
with that of various segments of the unexposed, comparable population
shows that tbe observed number of deaths among tbe miners is not
significantly greater. The rate for proved cases among tbe asbestos
miners (25.$ per 100,000} compares well with tbe rate of 22.5 per
ICO, 000 for the rest of the Province, and 2C. 6 per 100, 000 for aculi
males throughout tbe Pomwion of Canada. It also compares satisfacto*
rily wub rates of IT. 2, 2$. 5, and 28.0 obtained from various sources
for adult males in tbe United States. Finally, in this matter of com*
parison, it would appear that the worldwide experience of persons ex-
posed to asbestos dust is not worse with respect to lung cancer than that
of the unexpesed population.
The counties surrounding the asbestos .producing areas, and
in which it is presumed most of the asbestos miners live, have almost
identical mortality rates with those of eight counties widely scattered
?6.
through the Province, And Arc lower than those lor the rerr.Ainaer c.' the Province, And much lower than the rote lor Montreal.
Since 2940, there hove been 19 coses w which the diagnosis 0/ primary cancer of the lung may be considered to have been proved. Approximately ball 01 these cases were associated with asbestosts. Ail but one died in the recognised "cancer age" and at least one-third bad only the lightest exposure (category 1} to asbestos dust.
Conclusions
'
Os the basis of a careful and detailed study of what are
believed to be complete and reliable data, it seems fair to conclude
that the asbestos miners at Thetford Mines and Asbestos in the Pro
vince of Quebec do not have a significantly higher death rate from lung
cancer than do comparable segments of the general population. Despite
this, the results suggest that a miner who develops the disease asbes-
tesis does bav a greater likelihood of developing caneer of the lung
than a person without this disease. We suspect, however, that under
reporting of asbestosis cases bad led to a fallacious finding in this eon-
nection.
The death rate from lung caneer in the areas continguous to
the asbestos operations is comparable to that in areas widely scattered
thru'-igliOwt the Province of Quebec and is lower than m some urbanised
**#
tr.v Province.
caoz
n. The present study indicates that the effect ol cigarette
smoking is a much mere important consideration m the precursor, of lusg^aacer than is exposure to asbestos, and in that respect, it tends to confirm recent studies dealing with tbe effect of smoking.
The value of this investigation would be considerably en hanced by continuing the observation of the cohorts formulated herein on a year-by-year basis. It is strongly recommended that tbe chest x-rays of all workers be submitttd to an independent reading for the' diagnosis of asbestosis, since an inaccurately low incidence rate for this disease creates an artificaUy high relative incidence for lung cancer.
0209
78.
VII. BIBLIOGRAPHY
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i. Alascio, Escobar R. Bronchial carcinoma; review of two hundred cases. J. Internal. Coll. Surgeocs. 26: 375-J?9, September, 1956.
3. Allen, M.L. Bronchiogemc carcinoma associated with pneumoconiosis; report of two eases. J. Indust. Hyg. 18: 386*34?, November, 1934.
4. Amberson, J.8. Some clinical features of pneumoconiosis. New York Scat* J. Med. 49: 630*832, April 1, 4949.
5. American Cancer Society, lee. Cancer of the lung; ar. evalua tion of the problem. Proceedings of the Scientific Section, Annual Meeting, Nov. 3*4, 19S3. American Cancer Society, Inc. New York, 1956. 322 pp.
6. Anderson, C.S. and Dibit, J.K. Silicosis and earcmorr.a of the lung. J. Hygiene. 36: 185*204, March, 1938.
7. Andersen, R. J. Lung cancer yield in urban mass a*ray surveys. Proceedings of the Scientific Section, Annual Meeting, Nov. 3*4, 1953. American Cancer Society, Inc.
I. Ariel, I.M., Avery, ., Renter, L., Head, J., and
y*--
Langston, K. Primary carcinoma of the lung; clinical
study oi 1205 cases. Cancer. 3: 229*239, March, 1950.
9. Arkin, A., and Wegner, D.K. Primary carcinoma of the
lung; diagnostic study oi 135 cases in 4 years. J.A.M.A.
106: 567-591, February 22, 1936.
10. Au/ses, A.H. Primary carcinoma of the lung: a U-year survey. J. Mt. Sinai Kosp. 20; 212-226, SeptemberOctober, 1953.
11. Boeder. E.W. Asbcstosis. Deutsche mcd. Wochschr. 65: 407*406, Xiarch 17, 1939.
79.
12. Bar.yai, A.L. N'ontubercuinus disease* of the encs:.
.Jipringfieid, 111.. Charles C. Thomas, 1954. UJ9pp.
13. fianyai, A.L., and Peabody, J. tf. Pulmonary adenoma* tosis. Nontubereulous diseases of the ehest. Springfield, 111., Charles C. Thomas, 1954. pp. 416*422.
14. Baatenier, H., Denelin. H., Dtcoster, A., and Denoiin* Reubens, K. A clinical and pathological study of a case of pulmonary asbestosis. Arch. Beiges Med. Social*. Hyg., Med. Travial at Med.'Legale. 10:61*70, February, 1952.
15. Bauer, J.T. A review of the primary carcinomas of the
lungs and pleurae occurring is six thousand consecutive
necropsies. Bull. Ayer Clin. Lab. Pennsylvania Hosp.
3: 139*166, October, 1938.
_?
16. Behrens, W. Experimental asbestosis. Schwein. Itschr. Allg. Path. V. Bakt. 14: 275*297, 1951.
17. Behrens, 'V. Jr. The clinical picture and pathology of asbestosis. 2. Vnfallmed. u. Berufkrankh. 45: 129*140, June 15, 1952.
18. Bcrblinger, W. Increase of lung cancer and diseases due to dust inhalauon. Med. Xlin. 27: 1357-1342, September 11. 1931.
19. Bcrenblum. I. Irritation and carcinogens. Arch. Path. 38: 233*244, Oetober, 1944.
+>'
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