Document y0MXL0ZanJ3x21NOk3Z40ve6

Pergamon PIC: 50003-4878(01)00046-1 Hit., V|. 4i% Na 7. Pf I li-il*, JOTI t IWI B+tUj^ OtCupllriJlHj Hrl S<KrtJy PiblifclwJ bjt CUcvkt t'Ktwc Ltd. All nffeu niaW Case-Referent-Survey of Young Adults with Mesothelioma: I. Lung Fibre Analyses J. C MCDONALD**, B. G. ARMSTRONG*, C. W. EDWARDS, A. R. GIBBS'S, a M. LLOYD?, F. D. POOLEYj|, D. J. ROSSf and R. M. RUDD# ^National Heart and Lung InstUut-., Imperial College School d Medicine, London, UK; tLondon School d Hygiene and Tropical Medicine, London, UK; Royal Orthopaedic Hospital, Birmingham, UK; \llanddugh Hospital, Penarlh, If'ales, UK; j|University d if'ales, Cardiff, li'ales, UK; #St Bartholomew's Hospital, London, UK Objectives: Our study aimed to determine the lung tissue concentration of asbestos and other mineral' fibres by type and length in persons with mesothelioma aged 50 y r or less at time of diagnosis, compared to controls of similar age and geographical region. In this age group it was thought that most, but not all, wort;-related exposures would have been since 1970, when (he importation of crccidolite, but not amositc, was virtually eliminated. Methods: Eligible cases were sought from recent reports by chest physicians to the SWORD occupational disease surveillance scheme. Lung (issue samples were obtained at, autopsy from 69 male and four female cases, and mineral fibres identified, sized and counted . by electron microscopy, Fibre concentrations per p-g dry tissue were compared with similar estimates from a control series of autopsies of sudden or accidental deaths. Unadjusted, and adjusted odds ratios calculated by logistic regression, assessed relative risk in relation to fibre type, length and concentration. _ Results: Unadjusted and adjusted odds ratios increased steadily with concentration of era- cidolile, amositc, tremolite and all amphiboles combined. There was also some increase with chrysotile, but well short of statistical significance. Incremental risk examined in a linear model was as highly significant for all amphiboles together as individually. Short, medium and long amphibole fibres were all associated with increased risk in relation to length. Muliite and iron fibres were significant predictors of mesothelioma when considered without adjust ment for confounding by amphiboles, but, after adjustment, were weak and far from statisti cally significant. Conclusion: I n this young age group, amosile and erocidolite fibres could account for about SO*/, of cases of mesothelioma, and tremolite for some 7%. The contribution of chrysotile, because of low biopersistence, cannot be reliably assessed at autopsy, but to the extent that tremolite is a valid marker, our results suggest that it was small. The steep linear trend .in odds ratio shown by amphiboles combined indicates that their effects may he additive, with increased risk from the lowest detectable fibre level. Non-asbestos mineral fibres probably made no contribution to this disease. Contrary to expectation, however, some 90% of cases were in men who had started work before 1970; this was so whether or not amositc or erocidolite was found in lung tissue. Si 2001 British Occupational Hygiene Society. Published by Elsevier Science. Ltd. All rights reserved Keywords: mesothelioma in young adults; occupation; lung fibre analysis INTRODUCTION Received 26 January 2001; in final form 14 April 2001. Authorio whom correspondence should be addressed. Tel.: +44-20-735)-8934; fax: +44-20-7351-8091: e-mail: c.mcdonald@ic.ac.uk - The steady rise in mortality from mesothelioma in Britain since the 1950s, predicted to continue Tor some years to come, was investigated in the present study in persons, it? far as possible, aged 50 yr or less at time of diagnosis. It was argued that the occu- 5i3 SH 1. C. McDonald cl at palions and lung fibre content of these cases would mainly reflect exposure to asbestos since 1970, when the importation of crocidolite, but not amosite, was virtually eliminated. However,exposure to crocidolite would certainly have continued after that date, mainly as a result of asbestos removal and, as it later proved, almost all cases studied werein persons Fust employed before 1970. The investigation had two separate but related components. The first entailed identification of eli gible cases, followed by detailed recording of work histories and other relevant data. The second, which is the subject of this report, required collection of lung (issue samples taken at autopsy from as many of these cases as possible, together with similar samples for comparison from accidental or sudden cardiac deaths. . Procedures used in the ascertainmentof cases, rec ording of work histones and occupational analyses which form the background for the present paper are described fully elsewhere (McDonald el el., 2001, this issue). Eligible cases were sought from reports by chest physicians to the SWORD national work- related disease surveillance scheme and were obtained for 115 men and 13 women. Years spent by men in each occupation were compared with expected values from census data. Of 37 industrial occupations analysed, odds ratios were significantly raised in eight: five in the construction industry and the others in shipbuilding and the manufacture of cement and non-metaliic mineral products. Only four of the women had been employed in any industrial occu pation; the remainder included four in office work, two in nursing, two in sales and one in teaching. ttfETHODS Cose end control selection Cases included in the occupational study were fol lowed so far as possible until the end of 1997, by which time most of the i 15 men and 13 women with recorded work histories had died. Inquiry indicated that in 98 of these cases there had been an autopsy. The desirability of lung burden analysis with histo logical conFirmation of diagnosis was discussed with the pathologists responsible and as a result, lung tissue and tumour' samples were obtained from 69 male and four female cases. Histological review made independently by our two pathologists (CWE and ARG), both considerably experienced in the diagnosis of mesothelioma (Altanoos and Gibbs, 1997), con firmed that in all cases the diagnosis of mesothelioma was at least highly probable. So far as possible, lung tissue samples were obtained as referents from the same pathologists as the cases from accidental or sud den cardiac deaths of similar age, sex and region. As such cases were uncommon, this proved difficult, so the search was extended more widely. This resulted in a much larger number of samples,,bu( relatively few which met llic criteria of age and region com pletely. Mineralfibre flrinfjSO' The methods used Tor the preparation and cleclrpn- tnicroscopic analysis of fibres in lung tissue have been fully described elsewhere (Gibbs and Poolcy, 1996). In summary, small pieces of tissue were obtained from different parts of the lung from cither wet fixed specimens or paraffin wax blocks, depending on availability. The samples were weighed and then digested in 40% potassium hydroxide sol ution. A similar piece of lung tissue was weighed wet and dried to constant weight, in order to determine the wet to dry ratio. Tissue embedded in wax blocks was recovered using xylene and ethanol extraction, and then dried to constant weight before preparation. The digested tissue residues were washed, centri fuged, dispersed and then collected by filtration onto cyclopore filters (pore size 0.2 pm; diameter 25 mm). These were carbon coaled, die filters dissolved in chloroform, and the carbon filters mounted into gold electronmicroscope support grids for transmission electron microscopy. Random areas of the grid were examined at a magnification of x22 000. Fibres were identified, counted and sized until 100 or more had been accumulated, or a specified level of detection (0.2 fibres per pg) had been exceeded. All fibrous structures with an aspect ratio of 3:1 or greater were analysed to ascertain their elemental composition using energy dispersion X-ray analysis, ! Scartsdeal analysis The analysis was confined to 69 male cases, whose ages tanged from 36 to 52 yr. Of the 74 controls, 17 were aged five or more years outside this range and were excluded from further study, leaving 57 in all. The degree of matching by age and geographical region is shown in Table l.To allow for residual con founding conditional logistic regression was used to estimate (he odds ratios, stratifying by the five age groups and regions shown. The distribution of cases and controls by category of lung fibre concentration --0 (none detected), 0.1 0.9, 1-9.9, 10-99.9,100+ fibres per pg --was tabu lated for each specific fibre type, for all amphiboles, all asbestos fibres and for seven other types or mineral fibre. Relative risks were estimated relative to the zero fibre concentration group. In Older to allow for the effect of one fibre type when considering another, relative risks were also estimated, adjusting for other fibre types by including them simultaneously in the model. Models were also fitted which allowed for risk to vary continuously with exposure. Linear relative risk models were found to fit much better than the more commonly used log-linear models. For models including more than one' fibre type, linear-additive Controls Cases Controls Cases Lung fibre analyses of mesothelioma Table 1. Cases and controls included in analysis, by age group and region 36-39 2 2 4<W4 13 16 Age 45-49 19 33 50-56 23 IS Total 57 69 Scot and N 15 13 NiV and HE 16 14 Region Mid (E and N) II 17 Wales and SW London, SE and Total Anglia 10 5 37 9 16 69 J15 models fitted much better than the more usual exponential-multiplicative, (n these analyses, confi dence intervals were calculated using the likelihood profile method of Prentice and Mason (Prentice and Mason, 1986).The proportion of cases attributable to each fibre type was calculated from the linear model slope estimates according to the method described by Brunei (Btuzzt ct a!., 1985). RESULTS Asbestos fibres The distribution in cases and controls (Table 2) shows substantially higher concentrations in cases of all asbestos fibres, all amphiboles, crocidolite. amosite and, although rarer, tremolile; cases also had more chrysotile. Unadjusted odds ratios reflect these differ ences, with large values for all groups with concen trations of crocidolite, amosile and all ampliiboles, increasing with concentration. The odds ratios for tremolite were also elevated, but imprecisely esti mated and of limited statistical significance. There were moderately elevated risks with chrysotile fibres, but the association fell well short of statistical sig nificance. The estimated increment in relative risk'in the linear model was highest for crocidolite and, among amphiboles, lowest for tremolite, but with overlapping confidence intervals. Allowing for the effect of other fibre types on risk by entering all four in the model proved difficult, as odds ratios became very unstable. Therefore Table 2 shows the estimates for each specific' amphibole allowing for the effect of the other two, and for all amphiboles and chrysotile adjusting for each other. Mutually adjusted patterns remain broadly the same, but with differences between the three amphiboles Table 2. Distribution of lung fibre concentrations with grouped and continuous odds ratios Fibre type Concentration (per pg) Cases Controls Unadjusted OR Adjusted OR* Crocidolite Amositc Tremolite All amphiboles Chrysotile 0 0.1-41.9 1.0-9.9 10.0Lineac model* 0 0.1 --0.9 1.0-9.9 10,0Linear model" 0 0.1-43.9 LO-9.9 10,0- Linear model* 0 0.1 -0.9 LO-9.9 10,0Linear modeP 0 0.1-0.9 LO-9.9 10.0Linear model* 28 27 1L 3 13 23 26 7 55 13 t 0 6 26 28 9 14 2S 26 1 48 8 1 0 34 IS 5 0 51 6 0 0 23 24 4 1 19 21 16 1 1.0 5.3(2.0-14.3) 17S (2,0-L5S) V> 13.2(3.3-44,5) 1.0 5.6 (1.6-18.8) 24.9 (5.7-108) W 11.4(2.8-49.2) L0 2.2 (0.9-6.6) - * 6.9 (02-30.9) 1.0 92 (1.9-44.3) 64.7 (9.8-425) 55.8 (3.9-792) 19.4 (4.2-137) L0 I.S(0.6-3.9) 2.2 (0.8-62) - 0.1 (<0-l 2) 1.0 4.6 (1.3-15.5) 3.9 (0,3-40.4) W 40.0 (2.6-38S) 1.0 5.1 (1.4-IS.6) 17.9(3.5-91.4) W 14,3 (22-113) L0 2.3 (0.7-8.0) - -' 29.6 (C0-340) L0 8.8 (1,8^13.3) 59.9 (9.0-400) -- 47.6 <6.0->999) L0 1.9(0J-6.7) 2.2 (0,6-8.4) - 22 (<0->999) "Crocidolite, amosile and iremolile are adjusted for each other. Total amphiboles and chrysotile are adjusted for each other. "Average increment in odds ratio per fibre/pg. . 516 J. C. McDonald ct at. Table 3. Estimates of fractions of eases attributable to eacli significance (likelihood ratio test =5.9 on_2 df, fibre t>pc F =0-05). Fibre type Attributable fraction Unadjusted 95% Cl Adjusted* Otherfibres Croddolitc Amosite Tremolite 51% -' " 70% 12% AH amphiboles 86% Chrysolite 11% (38-56) (57-77) (1-181 (74-90 (CM3) 33% 46% 7% 84% 11% Seven types of non-asbestos mineral fibres were identified in alt but three of the 69 cases, and in all 57 controls. The detailed distributions are shown in Table 5. Mullite and iron were significant predictors of mesothelioma when considered without adjustment Adjustments as for Table 2. for the confounding effect of amphiboles, with which they were appreciably correlated (Spearman's rank correlation 0.28-0/3). After allowing Tor this con founding. the associations were weak and far from well within the bounds of chance. The model with statistically siguificant.The remaining five fibre types the three amphiboles included separately fitted the showed little evidence of association with mesothclidata no better than the model combining amphiboles. . oma, with or without adjustment for amphiboles. Table 3 shows the estimated proportion of cases attributable to each fibre type. The confidence inter vals for these estimates reflect uncertainty in the rela DISCUSSION tive risks, but not uncertainty in the selection of the The results of this study suggest that in the UK, a cases. Confidence intervals for adjusted proportions high proportion of deaths from mesothelioma in are not shown, as they could not be calculated young men whose working lives began in the 1960s, reliably. Although it is dear that a large majority of and were predominantly in the 1970s or later, resulted cases could be explained by the amphiboles including from crocidolite or amosite exposure. Although risk tremolite, as pure chrysotile fibres do not persist in per fibre was as high for tremolite as for other amphi lung tissue, their contribution is uncertain. boles, it was found less frequently, and so made little The effect of amphibole fibre length is examined contribution to explaining the cases. As tremolite in Table 4 with odds ratios calculated for three deposits often occur in proximity to chtysotile it can ranges: <6. 6-10 and >10 pm. Shorter fibres were be considered a more biopersistent marker Tot it. Thus more abundant than longer fibres, and as high concen the low proportion of cases attributable to tremolite trations of all fibre lengths tended to occur together would also imply a low proportion attributable to : (correlations from 0.6 to 0.91, discrimination was dif chtysotile, though appreciably less than the 20% esti ficult. Short, medium and long fibres were all associa mated in a survey of predominantly much older cases ted with mesothelioma risk; those longer than 10pm across Canada some 20 years ago (McDonald et at,, had the greatest Lnctement it risk per fibre, followed 1989). by medium (6-10 pm) and then by short (<6 pm), As had been observed in two previous studies with coefficients of 417, 116 and 9, mutually (McDonald it at., 1989; Rogers et at., 1991). long adjusted. The difference between the coefficients was fibres were associated with greater risk than shorter on the borderlines of conventional levels of statistical fibres, but as all sizes were usually found together. Table 4, Distribution of amphibole fibre concentrations by length, with grouped and continuous odds ratios Fibre length Concentration (per pg) Cases Controls Unadjusted OR Adjusted OR* a <6 pm 6-10 pm >10 pm 0 0.1-0.9 f.0-9.9 mo- Linear modd 0 0.1-0.9 I.O-9.9 10,0Uncar modd 0 0.1-0.9 1.0-9.9 10.0Lcncar modd 7 26 29 7 34 27 6 2 40 24 4 1 28 24 4 ' 51 6 0 0 55 2 0 0 14 5.7 (IS-22J) 41.9 (7.7-229) 33.6(2.7-419) 13.4 (3J-67.0) 1.0 7.2(2.4-21.1) n n 2SJ (7.1-106) 1,0 17.1 (3.6-81.9) tn CD 70.9 (14.1-517) 1.0 4.1 (1.0-17.1) 13.4(2.2-81.9) 3.6 (0.1-91.4) 9.3 (X.1-77,9) 1.0 2.9 (0r.a8-10.4) tn 1.0 4.8 (0.8-27.6) <n IT) 417 (I5-S-;>W) "One size fraction adjusted for Ute other two. ! I t i j I Mullite Controls Cases Iron Controts Cases Rulilc Controls Csses Muscovite Controls Cases Silica Controls Cases Kaolin Controls Cues AJurotna Controls Cases Lung fibre analyses of mesothelioma Table 3. Distribution of other fibres in cases and controls', details Concentration (per Jig) 0 0.1-0.9 1.0-95 10.0- 1 -1 8 7 37 It 24 34 20 29 7 8 37 21 1 0 12 34 II _ H 39 16 - 20 30 7 - 26 24 16 - 20 29 8 - 30 22 14 - 53 4 - 60 6 - - 51 2 4 0 58 7 0 1 S17 Total 57 66 57 66 57 66 57 66 57 66 57 66 57 66 the discrimination-was difficult. Risks associated with amphibolc concentration were close to linear and per haps independent of fibre type. Mineral fibres, other than' asbestos, showed little or no evidence of a causal association. There is evidence, however, that there probably always has been a low background inci dence of mesothelioma in hod) men and women unre lated to asbestos (McDonald and McDonald, 1993). The adjusted fractions attributable to amphibotes (84%) and chrysolite (11%) do not take this into account, but still leave 5% unexplained (see Table 3). The clear-cut findings from this study, with their considerable implications for fibre carcinogenesis and the public health, although strongly supported by a large body of epidemiological data (McDonald and McDonald, 1996)andby a recent comprehensive stat istical analysis (Hodgson and Damton, 2000), must be examined nevertheless for the possibility of errors or bias. First there are questions of case and control selection. Probably not more than 70% of mesotheli-' ana cases in the UK are reported to SWORD and lung tissue was obtained for analysis from only some 60% of the eligible cases reported. Although conceiv able, we think it improbable that a chest physician's knowledge of a patient's exposure history might affect whether or not a case were repotted, but not whether lung tissue at autopsy was later available for analysis. The selection of controls was certainly less than ideal, but without obvious bias in relation to the questions under investigation. More important is the fact that the electronmicroscopicanalyses were made, and results recorded, for tissue specimens, identified only by serial numbers unrelated to case/control status. The most serious and fundamental source of poten tial bias is the fact that mineral fibres vary in their biopersistence, and in particular that chiysotile is far less durable in lung tissue than crocidolite, amosile or tremolite. As a result, findings for chiysotile at autopsy will reflect recent exposures of little etiolog ical importance rather than those many years ago, whereas those for amphibolcs will do the reverse. From animal studies it seems likely that carcinogenic ity results mainly from biopersistence (Searl rf at.. 1999; Miller et at. I999a,b), and if this is the case the clearance of chrysolite does not invalidate the conclusions from fibre analysis, in humans the evi dence that durable agents arc more carcinogenic is strong although indirect, consisting of extensive epid emiological evidence tha t exposure to suchbiopersistent agents as crocidolite, amositc, tremolite and erionile is followed by a far higher incidence of mesothelioma than occurs after chrysotile exposure (Hodgson and Damton, 2000). The. further indications that chrysotile as mined and milled and used commer cially is often contaminated with fibrous tremolite help to complete the picture. Tremolite fibres alone have been shown to cany a high risk of mesothelioma (McDonald tt at., 1986) and that their level of con centration in the various chrysotile mines of Quebec is correlated with the incidence of this disease (McDonald and McDonald, 1997). Acknowledgements--This research was conducted with the he]p of chest physicians, pathologists and coroners throughout the United Kingdom, and was supported try giants from the Health and Safety Executive and the Wellceme Trust. 513 J. C. McDonald ct uL REFERENCES Attanoos RL, Gibbs if!. Padiofogy of malignant mesotheli oma. Hisiopathology 1997:30:403-18. ftniTTi p, Green SB, Byar DP, Brintou LA, Scliairer C Esti mating the population attributable risk for multiple risk fac tors using case-control data. Am J Epidemiol i985;l 22:904-14., Gibbs * . Poolcy FD. Analysis and interpretation of inorganic mineral particles in `king* tissues. Thorax 1996;51:327-34. Hodgson JT. Damion A. The quantitative risks of mesotheli oma and lung cancer in relation to asbestos exposure. Am Occup Hyg 2000:44tS):565-60l. McDonald JC, Armstrong B, Case B, Doell D. McCaughey WTE, McDonald AD* Sibastier P, Mesothelioma and asbes tos fibre typo: evidence from lung tissue analysis. Cancer 1989;63:1544-7. 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