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FILE NAME Kent KNT DATE 1956 Feb DOC KNT146 DOCUMENT DESCRIPTION Journal Article - Epidemiological Tests of Theories on Lung Cancer Etiology Ot eg oe trey. Celgene te bole oe gn Volume 71 Number 2 FEBRUARY 1956 Published since 1878 Epidemiology of leukemia --PHR review 0.000000 Gilcin E. Mendors Page 103 CONTENCONTENTS TS Clues to suicide 0000 be eee ee eee, Edwin Shneidman and Norman L. Parberow Edwin Edwin S. Shneidman Shneidman S. Parberow e Parberow Ca, rdiovascular diseases and public health oo 0000000. John W. Ferree The The The climate epidemic epidemic climate epidemic PHR epidemic climate PPHRHR Winston H. Price review revireevwiew review . . 109 a 115 125 112255 Unfinished business in maternal and child nutrition . Marjorie M. Heseltine The use of insecticide treated cords for housefly control _ . John W Kilpatrick and H. E. Schoof Man's emergence toward health The C.-E. A. Winslow lecture 1955 Henry van Zile Hyde Public health in Pennsylvania , Berwyn F. Mantison 139 1.11 Epidemiological tests of theories on lung cancer etiology 163 William Haenszel Haenszel Health services in civil defense- A symposium symposium .. a Biological considerations in atomic defense Edicin G. illiams and Samuel C. Ingraham 11 Radiological defense 0 |. be Simon Kinsman 173 173 181 Chemical weapons 00 14 Harry P. Kramer : 1180 HEALT 1180 HEALT 2 " * < an , 79* frontispiecfero-ntispiece- Continued p} A laboratory technician determines clotting time information necessary to the safe use of anticoagulant drugs See story of the American Heart Association on page 115. Epidemiological Tests of Theories on Lung Cancer EtiologEytiology By WILLIAM HAENSZEL Q UESTIONS on the etiologies of lung cancer cannot be resolved by a single de- cisive experiment or set of observations and a deals more with the ideas underlying a set of studies than with the tactical details ofany single study single study is not the natural unit for disenuss- ing the epidemiology of this disease The major major Increase in Lung Cancer . concern must be with the interrelationships of If no real increase in king cancer existed all findings and their collation to see whether a associations between lung turer and expoziti expoziti chain of evidence stronger than any single com- to atmospherie pollution eiga He smoking or ponent part can be forged Information on a other exogenous agents recently introduced into proposed etiology cannot be assessed without the environment would be suspect as not point- relating it to both positive and negative findings ing to possible etiological relationships A few on alternate possibilities drawn from still maintain that the recorded increase animal experimentation and other laboratory work work persons in lung cancer incidence and mortality is fieti- % Also well as from epidemiological studies tions and has resulted from improved diagnosis with a subject under such active scrutiny as 1 but this is no longer a popular position lung cancer it is difficult to attempt to divorce 2 Among the reasons for accepting a real facts already established from interpretations in increase lung cancer mortality are the sex which may either be stated explicitly or merely differences in rate of increase and the magni- be implied by investigators through their choice tude of the current continuing increase < of specitic studies to be pursued Under these One purpose for inquiries on the increase conditions a better perspective on epidemiolog- in risk would be to provide more precise quan- icalissues in lung cancer studies may begained titative estimates than are now available from possible by viewing themin the perspective of data which later useful future work Since interrelationships of indi- mortality may prove for reconciliation with numerical measures of vidual findings are the main concern this paper exposure to suspected agents For this reason anyone proposing to study the effect of possible Mr. Haenszel is head of the Biometry Section misdiagnosis of I^,,ngcancer as tubercul^sis4 Biometry and Epidemiology Branch National or some other cause should relate these effects Cancer Institute Public Health Service He pre- to data produced by the death registration sys- sented this paper at joint session of the Biometrics tem Samples of deaths from hung cancer and Society and the Institute of Mathematical Statistics other causes taken from vital statisties sources Chapel Hill C. April 23 1955 could be compared with autopsy protocols and other diagnostic evidence Evaluation of the Vol 71 No. 2 February 1956 163 e two sources of error in official deaths from other statistics a causes erroneously recorded are not helpful to the contrary they may sug- as lung cancer and b lung cancer deaths at- tributed to other gest situations in which data can be collected and tested causes would be rendered difficult by the selective character of autopsy Occupational Carcinogens statistics However the effort should be made Carcinogens useful useful minimum objective would be to deter- There is mine how many lung cancer general agreement on the etiological diagnosed at cases remain un- significance of several occupational present Farber reported that in series of 1,070 morphologically proved cases and such findings have been importaenxtposinureesstablishing the of bronchogenic carcinoma 61 principle of multiple etiologies positively diagnosed percent were not for lung cancer Long observations of ame, prior to autopsy 5 Un- closed populations have mee doubtedly many of these dentlis were not re- that the convinced most people corded as lung cancer on the death certificate Schneeberg and Joachimsthal miners 7 and certain groups of chromate workers ee 9 10 were subjected by virtue of their Rw Environmental Agents occu- pations to excessive lung cancer risks The noe The working hypothesis for most investiga- evidence on chromate workers is purely epi- tors has been that the probable causes of demiological not confirmed by animal experi- on cancer are to be found Jung mentation and was first suspected on the basis among environmental of clinical observations Although inves agents 2 The association of the high prevalence of cancers for several other sites par- tigators have deduced from the many Joachimsthal Schneeberg and ficularly the mouth with specific customs found observations that radiations emit- only in certain parts of the world ted from radon were responsible Lorenz felt strengthens the belief that direct contact with known or that the case had not been firmly established and that other possibilities possibilities such as dust suspected carcinogens may be involved 6 On the niosis had not been pneumoco- assumption that agents with conclusively ruled out 11 opportu- nity for direct contact with lung tissue are the Excess lung cancer risks detected by exami- nation of most likely candidates efforts to establish occupational mortality data such as etiological relationships between lung cancer data on workers employed in the preparation of coal tar products and producer and environmental agents have been directed into three have also been gas 12 main areas a airborne agents en- generally accepted as reflecting countered in special occupations b atmos- an etiological relationship between lung cancer pheric pollutants particularly those and some suspected carcinogenic agent in these from combustion of resulting hydrocarbons and c products Nor is there any great disposition to question the status of agents detected smoking of tobacco by clinical To assert that an agent is observations and retrospective retrospective studies of lated to etiologically re- lung cancer simply implies that its re- anoval from such as arsenic dust nickel carbonyl asabgeesntotss dust and coke oven fumes a defined population will result 13 When the ultimately in marked reduction of lung ean- study results are reviewed to pick up tional exposures which occupa- cer The population must be defined in a man- appear repeatedly the ner which safeguards against an effect danger of being misled by highly unusual re- produced merely by the process of selectionbeainndg sult in single study is minimized Additional classification The concept does not occupational risks will no doubt be demon- tailed specification of a mechanism require de- strated in the future However because of the the effect producing Goldberger's finding that pellagra be prevented by diet was less small numbers of workers exposed the further denumeration of very restricted types of risks may no equase subsequent work led to the valid be- will not be crucial in working the of the vitamin B3 identification logical details of lung epidemio- tinic complex and finally to nico- would not cancer This statement acid as the effective agent This state- apply to the common and widespread ment does not imply that ideas on mechanisms agents contributing to atmospheric pollution including hydrocarbon combustion products 164 Public Health Reports such as industrial and heating plant wastes and motor vehicle exhausts Atmospheric Pollutants To date atmospheric pollution theories have not been well documented by demonstrations of excess risk among workers with heavy exposures to common atmospheric pollutants such as may exist in railroad yards oil refineries and congested urban areas With the advent of group insurance and pension plans the methodological problems of such inquiries have become much simpler Several cohorts can be located for study The National Cancer Institute is fol- lowing a group of 1,100,000 railroad employees who have been in the industry 10 years or longer including station office yard and shop employees as well as train crews Rather detailed occupational histories are available and with the accumulation of mortality data over several years such specific points as the effects of dieselization prolonged exposure to smoke in railroad tunnels and metal dust exposures in shops may be looked into The important feature is that work histories and exposures be specified in some detail Significant effects may be diluted and overlooked by considering only gross company or industry experience The widespread use of petroleum products makes it very desirable to gather data on workers in that industry Some medical departments of the major oil companies have staffs well equipped to undertake such studies The major problem here as elsewhere is to secure access to company records and to rearrange data organized to meet other administrative needs In areas where petroleum operations are concentrated data might be collected on geographie rather than an industrywide basis At least one study is under way in Oklahoma which may yiell some information on lung cancer risks among oil industry employees Those advancing atmospheric carcinogen theories have pointed to the sizable urbanrural differentials in lung cancer risk 14 although some further assumptions are required to reconcile this hypothesis with the great excess risk observed among males The presence of carcinogenic substances urban atmospheres has been repeatedly demonstrated by experi ments with mice 15 16 Further epidemiological work has been hampered by the inability classify individuals in the general population quantitatively with respect to atmospheric exposures Meaningful histories are hard to collect and in mobile populations problems of classification by residence histories become complex When leads on specific types of atmospheric pollutants are obtained from studies of special situations the way may then be opened for return to the problem of reclassifying the general population with respect to special exposures with greater chance for success Smoking of Tobacco Although at least 14 retrospective clinical studies 17 have reported on the association of smoking and lung cancer these studies have been criticized on variety of technical grounds The objections advanced cover such points as interviewer bias interviewers in some studies knew the identity of lung cancer patients aud controls at the time of interview and bias arising from selection factors associated with hospital admission in most studies only hospitalized lung cancer patients were interviewed However the objection based on knowledge of the identity of patients and controls ignores the evidence of Doll and Hill 18 that males erroneously interviewed as hug cancer cases as established by later events showed smoking histories characteristic of the control rather than of the lung cancer series Because of possible selection factors involved in taking up the smoking babit some feel that the tolerolung cancer associations reflect associations with other common but still unidentified factors The present data on associations between smoking and lung cancer are the most extensive and afford the most opportunities for discussing additional studies For orientation the type of evidence now on hand may be compared with the epidemiological findings for cholera pellagra and dental caries all diseases in which animal experimentation played a minor role at least in the early phases of the investigation 19 25 On review the basic core of associations ou smoking and lung cancer must appear as im- pressive as any produced in these other investi- Vol 71. No. 2 February 1956 370566-58--5 165 oe gations However lung cancer does not present the features of geographic localization charac- teristic for cholera pellagra and the absence of dental caries which made it possible to elaborato in a rather straightforward manner the basic associations with water supplies suspected of contamination cholera diet pellagra and iluoridated water dental caries with cor- roborative detail and combinations of isolated special situations Such detail is helpful in ruling out some association as not significant etiologically in this manner for example the associations between cholera and altitude within kulon kuulon and l^tweenpellagra and mill village occupations could be discarded as not significant For lung cancer there are as yet no counterparts for example to the cholera patient in an isolated rural area who regularly sent for water from the famous Broad Street pump 19 to the absence of pellagra among doctors nurses and attendants in mental insti- tutions although the disease was common among patients to the peculiar age distribution for pellagra in children's institution where the disease was limited to children between the ages of 6 and 12 to differential attack rates for dental caries by gradations of exposure to Huoridated supplies among natives and mi- grants and to the sequence of dental events fol- . lowing shifts in the source of a community water supply Collection of such details generally results from the study of populations This is one of the reasons why forward studies on lung cancer among defined population cohorts are so important Furthermore the epidemiological models for cholera pellagra and dental caries have been put to the test in the successful application of control measures For pellagra only the addi- tion of meat and milk to the diet was involved 26 Fluoridation effects could be observed under controlled conditions because of the happy accident of public water supplies if private wells were the only source of water the problem would have been complicated by selfselection of families fluoridating their own supplies The test of Snow's conclusions on cholera 19 which required implementation through administrative decisions on methods for control of public water supplies occurred much later more than 10 years after he had formulated them The right combinations of circumstances to permit such straightforward tests of most of the proposed lung cancer etiologies are not present now Thus the immediate lines for further work on the nature and meaning of the smokinglung cancer associations are to develop reasonable facsimiles to tests by control measures and to assemble supporting corroborative details from population studies not overlooking any negative evidence which may appear Substitutes for Direct Tests As a substitute for a direct test by control measures of the smoking cancer model one may look for groups in which smoking is either proscribed for religious reasons or does not otherwise form part of the cultural pattern Two of the four basic study elements required are at hand data on the distribution of smoking habits in the United States population collected as part of the Current Population Survey . for February 1955 and data on lung cancer mortality from publications of vital statistics offices The major problems would be to secure the cooperation of the groups selected and to develop procedures to obtain the coun- terparts of these data for their memberships To avoid artifacts which might be introduced by classification procedures the primary test must be whether the overall lung cancer mortality in the group studied was markedly less than for an appropriate segment of the popula- tion of the United States and commensurate with differences in the smoking patterns To this other refinements may be added such as observing whether mortality differences between the study and control populations disappear when specific comparisons are made by amount of tobacco smoked The limited number of countries which can provide reliable diagnostic data on causes of illness and death has discouraged similar studies of groups abroad which have unusual smoking patterns However special study situations may be encountered One illustration is cited without judgment as to its intrinsic merit The director of the Hadassah medical organization recently reported the absence of a single case 166 Public Health Reports of lung cancer among Yemenite Jews in Israe during the past 15 years and he further ob served that they did not smoke cigarettes but used a form of Oriental water pipe 27 Israel is a country with western standards of medical care and this lead may be worth pursuing In these matters the importance of reviewing tho primary sources of population morbidity and mortality data should be stressed Other clues may lead indirectly to population groups with unusual smoking histories For example Steiner 6 on the basis of necropsy evidence in Los Angeles has found a possible . exception among Mexicans to the usual sex ratio for lung cancer the proportion of Mexican women with lung cancer at autopsy approaches the proportion for Mexican men This suggests the need for further studies among Mexicans to confirm the facts and to uncover possible reasons for the aberrant sex ratio for lung cancer This might conceivably lead to the finding of a group of unusually heavy smokers among women a useful contrast to the experience of abstainers Corroborative Details Additional details on the nature of the smok- lung cancer relationship should be assembled from scale forward studies These possibilities were obviously in the minds of those who planned the AmericaCancer Society and the National Cancer Veterans Administration studies Both study groups consist mainly of men between the ages of 50 and 69 the ages of highest lung cancer inci- dence One approach is to expand the evidence on the nature of the association by detailed cross- classification Epidemiologists have long accepted the principle that the etiological signifi- cance of an association is enhanced if it can be shown to persist within a variety of uni- | verses The National Cancer Institute ans Administration cohort can be subdivided with respect to occupation and industry By lengthening the observation period to several years further tests can be applied in both studies including checks on the consistency of regression relationships between lung cancer mortality and amounts of tobacco smoked for several occupational groups and for urban and rural residents Additional tests can be pursued by relating age at death to age started smoking to see if any consistent pattern emerges Studies Among Women Unfortunately for study purposes the spread of age started smoking is not too great among men and it may be hard to assemble sizable cohorts for the more unusual combinations of year of birth and age started smoking Women would be more promising subjects since women of all ages began smoking in large mumbers during the 1930 decade and duration of smoking by women is not so closely tied to chronological age For this reason more prospective and retrospective studies on smoking and lung cancer among women would be rewarding In addition to the one series of studies on smoking among women reported by Doll and Hill 28 two nut spective studies are known to be under way The relative rarity of lung cancer among women imposes severe study handicaps and has undoubtedly deterred other efforts Potential cohorts for followup would include employed women covered by group life insurance policies To minimize turnover and loss to observation it would be desirable to restrict the cohort to employees with several years service Studies of lung cancer among women should establish what part if any of the sex differen- tial in lung cancer mortality or incidence dis- appears when comparisons are made specific for smoking class The fragmentary fragmentary Doll data suggest that a good part but not all of the sex differential may be accounted for in this manner Indirect Checks Retrospective and prospective studies may be viewed as efforts to secure etiologically meaningful data which official vital statistics sources cannot provide since they are limited to classification by standard demographic variables There is another transitional bridge by which vital statistics data on lung wancer deaths can Vol 71 No. 2 February 1956 167 utilized By taking information on smoking patterns in the general population collected in Current Population Survey for February tional factors which may be engendered by the processes influencing persons to take up smoking 1955 and applying to them the data on absolute and relative lung cancer risks by smoking class as reported in the preliminary results of the American Cancer Society study 29 and in several retrospective studies 30 the ex- In dealing with lung cancer where prospects for tests of etiological relationships by trial of control measures are remote other hypotheses however unlikely and the collection of evidence to support or discredit them should be en- pected distribution of lung cancer deaths cau couraged The pursuit of other lines of in- be computed by sex urban or rural residence vestigation will be useful If results are posi- geographic region and broad occupational tive another effect of lung cancer will have ; groups on the assumption that risks by smoking been discovered if negative they will buttress HE class in the groups studied hold also in the the interpretations applied to effects already total population Comparison of the observed known AE NE and expected numbers of deaths would then Gilliam in a general discussion of chronic A show how much of the prevailing variation in disease epidemiology alluded briefly to a va- roa: lung cancer mortality can be accounted for by riety of items investigated by him in a study eine considering smoking histories In this manner of lung cancer patients and controls using the A some useful consistency checks on the smoking- retrospective history method 31 These Sten lung cancer model would be provided items ranged from color of eyes and use of den- Such consistency checks need not be confined to smoking smoking histories The Current Population tures to histories of illnesses and use of general anesthetics As he hastens to say such indi- Survey material illustrates an economically feasible means for remedying some deficiencies vidual findings cannot be used for any generalizations However it may be worth while to in standard population classifications Al- inquire systematically into other findings col- though many investigators have expressed the red for procuring information on the popula- lected but never deemed worthy of 3 report Several of the other early retrospective studies tion distribution of characteristics under study were shotgun inquiries and collected informa they have often been deterred by the cost tion on a variety of suspected agents and ex- Probability sampling methods for gathering such data can provide a powerful tool to the posures Collectively these results might prove useful for testing and discriminating between between epidemiologist hypotheses and the planning of further studies Several studies exploring characteristics dif- Other Possible Factors ferentiating smokers and nonsmokers may bo Turning from suspected environmental agents with properties which permit direct contact with lung tissue several possible causes of lung cancer remain There is the class of environmental agents which do not come in di- rect contact with lung tissue Closely related would be possible tissue changes induced by virus and other infectious agents Constitutional susceptibility might also be considered If some persons have a predisposition to attacks on lung tissue by some morbid process the rise in lung cancer might be due to the suppression of competitive respiratory causes such as tuberculosis and pneumonia Finally there is the possibility of the association of smoking with other physical psychological and emo- expected The question of differences between the two groups arises because smokers select themselves smoking is not a treatment which can be studied experimentally by randomized application to a population There is a wide range of possibilities for retrospective studies on the physical psychological and emotional attributes of smokers and nonsmokers The demonstration of an item as being associated with smoking history is essentially a screening device The further test is whether the item when applied to a population produces differ- ences in lung cancer risks equal in magnitude to those yielded by smoking history classifications if smoking history is uncontrolled or whether an effect is observed when smoking history is controlled by classification 168 Public Health Reports fo epee mene mms Ya Re etme eT RNEW ee oe ee ene ps a einre ey ig ae eee ee Association With Other illnesses " Some theories on the subsequent increased risk of lung cancer among persons with histories of respiratory illnesses such as influenza pnen- monia bronchitainsd tuberculosis based usu- ally on clinical and pathological impressions have been reviewed by Doll 32 who continues on to point out some observations inconsistent with these theories No associations of lung cancer with the presence or absence of an ante- cedent illness have yet been established by observations on populations through the use of retrospective or prospective studies Retrospective studies are handicapped in this field because patients with lung cancer and other respiratory disorders apparently recall previ- ous respiratory ailments more readily than do other persons There are some possibilities for forward studies on cohorts known to have re- covered from specific illnesses free from the recall bias in the retrospective approach which may be exploited For example records can be assembled of World War I veterans who had influenza and pneumonia in 1918 These veterans can be traced forward in time to determine their hung cancer mortality experience A study of British veterans 40 lias been published recently From civilian life one could draw on recovered pneumonia cases reported to health departments in the 1930 decade when these agencies had active programs based on pneumococcus typing and distribution of serum If excess lung cancer mortality among such groups were demonstrated this would not necessarily be a result of effects of antecedent illnesses If constitutional predisposition of lung tissue were a factor the rise in lung cancer mortality might be due to the suppression of tuberculosis and pneumonia as causes of death If genetic basis for constitutional predisposi tion to lung cancer were postulated other tests could be devised One approach would be to assemble lists of relatives of diagnosed eases of lung cancer for followup to determine lung cancer mortality Lists of familial contacts could be assembled from records maintained in inberculosis control programs Investigations of this character might be undertaken more readily in some European countries where pop- ulation mobility is low and more comprehensive population record systems exist Retrospective and Forward Studies The preceding sections have emphasized the wide range of possibilities for the use of retro- retrospective and forward study techniques Retrospective history studies use as their point of departure diagnosed cases of a disease and matched controls and compare antecedent events in their previous histories Prospective or forward studies start with the assembly at a fixed point in time of defined cohorts classified with respect to certain attributes trace them forward in time and note events occurring subsequently Perhaps the major criticism of retrospective * studies for lung cancer has been that diagnosed cases have generally been drawn from hospital populations Positive association between two diseases not present in the general population may be produced when hospital admissions alone are studied because persons with a combination of complaints are more likely to require hospital treatment 34 Smoking is not an illness and for lung cancer it is difficult to see how the smoking history could have any influence on hospital admission Lung cancer is serious disease normally requiring hospitalization and roughly fifths of all diagnosed cases are hospitalized 35 The proportion is even higher when microscopically confirmed cases alone are considered There would have to be extraordinary differences in smoking histories between hospitalized and nonhospitalized patients and controls to upset inferences drawn from hospitalized cases 36 So far the results of forward population studies on excess lung cancer risks among smokers as compared to nonsmokers have agreed in general with those of the retrospective studies This suggests that biases entering into the selection of hospitalized cases and controls studied retrospectively retrospectively are probably not the source of the associations noted The fundamental assumption underlying ret rospective studies and the estimation therefrom therefrom of differences in risks between population groups is that the diagnosed cases and controls each be representative of the quiverse chosen Vol 71 No. 2 February 1956 369 for investigation Although there are precan- effects on tions which can be taken in devising a sampling mortality experience exist as in the case of ordinary policyholders it is well known plan this representative property cannot be guaranteed merely from internal examination that the selection effects of physical examina- tions e of a single set of data One must be guided on on mortality experience wear off quickly very conservatively in 10 years or less 39 this point by the comparison of results from usually in about 5 years If there is Nen several studies and judgment as to the possible any ques- tion about the prospective study results the hone biases operating in any setting association of on - Ne Forward population studies have been smoking and lung cancer being ques- affected by selection the conservative course Ae tioned on the grounds that the cohorts have not would be to discount the first few poate been selected by probability sampling methods ence and to years experi- voi that individual individual require that the early results be con- rete study results cannot be gen- firmed by later experience after selection effects Ae eralized to Lae total population The expense have worn off anew re involved in tracing cohorts drawn from the gen- The collation of experience from several eral population by probability sampling meth- studies is also ods would be great and most investigators have a safeguard against error in generalizing from forward studies on lung cancer been forced to look for populations followed Data from prospective studies be sub- routinely for other purposes such as persons may classified by other population characteristics covered by employment or insurance benefits benefits The criticisms of unrepresentative sampling and further checked for internal consistency With these would appear to disregard the experience avail- precautions the dangers of drawing inferences from forward and retrospective able from actuarial sources There are two stulies inapplicable to the general population commion types of insurance ordinary poli- seem rather remote cies which require applicants to pass a physical examination and industrial policies which undergo some underwriting selection but re- Summary quire no physical examination Policyholders would scarcely meet the usual criteria for representative samples The Metropolitan Life Insurance Co. has published extensive data on the mortality experience of their industrial policyholders and finds rather close agreement with the mortality experience of the general population after appropriate adjustments for age sex and race composition 37 Data drawn from actuarial experience and reported in sugh sources as Length Length of Life 38 and The Statistical Bulletin a monthly publication of the Metropolitan Life Insurance Co. indicate that the relative patterns of mortality with respect to cause age sex race and geographical region in insured populations have their coun- terparts in general mortality experience despite some differences in magnitude of rates The co- horts assembled for smoking and lung cancer investigations do not appear to have been sub- jected to more rigorous selection than that en- countered by industrial policyholders nor is there reason to believe that the selection effects which did exist discriminated between smokers and nonsmokers Even when stronger selection The size of the lung cancer problem as indicated by the number of lives at stake and the economic implications of any potential control measures which might later be advanced should not blind investigators to the many possibilities for studies similar to those on other chronic diseases which have yielded some of their secrets to the epidemiological approach Diseases showing pronounced variations in risk among population subgroups are the more amenable ; to epidemiological study and lung cancer falls into this category Studies on human populations should continue to play an important role in delineating possible etiological relationships for lung cancer the mechanisms for which couki then be elaborated by animal experimentation Progress must come by the checking of the several results of epidemiological studies animal experimentation and other laboratory findings The issues will probably be settled by an evolutionary process as was the fluoride- dental caries relationship Gradually the meaning of certain associations will become accepted Dissent will die off and the debate will shift to the many other points in any La anny maw pyle = te, 170 _ Public Health Reports nae ne pe e nne voneteenes * epidemiological models still requiring elaboration . 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Prev & Social Med 9 62-72 1955 Ninth Annual Seminar on Seafood Sanitation ; bacteriologists The ninth annual Seminar on Seafood Sani- tation sponsored by the Virginia and Mary problems in the new Chesapeake Bay clam industry preservation of food by radioactive land State Health Departments was held in sterilization and Solomons Md September 27- 1955 More a discussion of the relative than 50 merits of State certification of persons attended the 5 sessions which ~ breaded seafood processors of included an inspection of an house and a visit by boat to packing clam Included in the agencies represented in the ing area on the Patuxent River harvest- discussions were State health departments The first Seminar of Maryland Virginia South Carolina on Seafood Sanitation was held in 1916 because seafood sanitation Georgia and the District of Columbia New spe- cialists found that their work required broad York State Department of Conservation Maryland county health departments which date technical knowledge In addition have seafood to the common food plant sanitation problems and Drug sanitation programs the Food Administration and the Public they were concerned with the construction and Health Service and the Fish and operation of municipal and private sewage Service The Wildlife disposal works they had to make seafood industry was repre- cal hydrographic and bacteriologi- sented by officials of the National Fisheries sanitary surveys of growing areas and they were obliged Institute the Oyster Institute of North Amer ica and the Oyster Growers and Dealers Asso- to apply the results of these studies to decisions ciation of North America Inc. ve * on the suitability of an area for shellfish cul- a ture The seminar has William Ballard president of the Oyster Pee where provided a forum Growers and Dealers Association of North ae sanitarians and sani- America Inc. and tary engineers working with seafood sanitation operator of one of the in the Chesapeake Bay area world's largest shucking and packing te formation ou such can exchange in- plants told of his industry's dependence on problems of mutual sanitation and expressed the gre interest opinion that the Many seafood sanitation problems en- future of the seafood industry rested with the accomplishments of the fisheries research countered by county State and Federal per- scientists and with the sonnel were discussed at the day meeting These included sanitary surveys of shellfish specialists seafood sanitation i. growing areas general food plant sanitation The participants recommended that the health departments of Maryland and sanitation of shucking plants sanitation Virginia problems in the crabmeat industry sanitary sponsor another seafood sanitation seminar in 1956 172 , Public Health Reports