Case-referent survey of young adults with mesothelioma: I. Lung fibre analyses

Objectives: Our study aimed to determine the lung tissue concentration of a sbestos and other mineral fibres by type and length in persons with mesothe lioma aged 50 yr or less at time of diagnosis, compared to controls of simi lar age and geographical region. In this age group it was thought that most , but not all, work-related exposures would have been since 1970, when the importation of crocidolite, but not amosite, was virtually eliminated. Methods: Eligible cases were sought from recent reports by chest physicians to the SWORD occupational disease surveillance scheme. Lung tissue samples were obtained at autopsy from 69 male and four female cases, and mineral f ibres identified, sized and counted by electron microscopy. Fibre concentra tions per mug dry tissue were compared with similar estimates from a contro l series of autopsies of sudden or accidental deaths. Unadjusted, and adjus ted odds ratios calculated by logistic regression, assessed relative risk i n relation to fibre type, length and concentration. Results: Unadjusted and adjusted odds ratios increased steadily with concen tration of crocidolite, amosite, tremolite and all amphiboles combined. The re was also some increase with chrysotile, but well short of statistical si gnificance. Incremental risk examined in a linear model was as highly signi ficant for all amphiboles together as individually. Short, medium and long amphibole fibres were all associated with increased risk in relation to len gth. Mullite and iron fibres were significant predictors of mesothelioma wh en considered without adjustment for confounding by amphiboles, but, after adjustment, were weak and far from statistically significant. Conclusion: In this young age group, amosite and crocidolite fibres could a ccount for about 80% of cases of mesothelioma, and tremolite for some 7%. T he contribution of chrysotile, because of low biopersistence, cannot be rel iably assessed at autopsy, but to the extent that tremolite Is a valid mark er, our results suggest that it was small. The steep linear trend in odds r atio shown by amphiboles combined indicates that their effects may be addit ive, with increased risk from the lowest detectable fibre level. Non-asbest os mineral fibres probably made no contribution to this disease. Contrary t o expectation, however, some 90% of cases were in men who had started work before 1970; this was so whether or not amosite or crocidolite was found in lung tissue. (C) 2001 British Occupational Hygiene Society. Published by E lsevier Science Ltd. All rights reserved.