THE EPIDEMIOLOGY OF MESOTHELIOMA IN HISTORICAL CONTEXT

Primary malignant mesothelial tumours were recognized by pathologists before asbestiform minerals (chrysotile, crocidolite and amosite) were mined commercially, The discovery, 40 yrs ago, of a causal link with crocidolite and the wide-ranging epidemiological studies which followe d are the subject of this review. Early case-control and descriptive s urveys, supplemented by cohort studies in insulation workers and chrys otile miners, quickly demonstrated major occupational and geographical differences, with high risk in naval dockyard areas and in the heatin g trades, In the 1980s, reliable cohort surveys showed that in mining and in the manufacture of asbestos products the mesothelioma risk was much higher when exposure included crocidolite or amosite than chrysot ile alone, However, qualitative and quantitative information on exposu re was too often inadequate for this evidence to be conclusive, Well-c ontrolled lung fibre analyses have reduced these deficiencies and demo nstrated the probable implications of the greater biopersistence of am phibole fibres, Chrysotile for industrial use often contains low conce ntrations of fibrous tremolite, which may well explain the few cases o f mesothelioma associated with this type of asbestos. Progress in this field has been much retarded by controversy, for which the 20 year ga p between the availability of reliable estimates of risk for the. mini ng of chrysotile and that for crocidolite or amosite may have been lar gely responsible.