Lung cancer risk, silica exposure, and silicosis in Chinese mines and pottery factories: The modifying role of other workplace lung carcinogens

Background Aims of our study were to explore whether and to what extent exp osure to other lung carcinogens, or staging and clinical features of silico sis modify or confound the association between silica and lung cancer Methods We used data from a nested case-control study, conducted in the lat e 1980s in 29 Chinese mines and potteries (10 tungsten mines, 6 copper and iron mines, 4 tin mines, 8 pottery factories, and I clay mine), that includ ed 316 lung cancer cases and 1,356 controls, matched by decade of birth and facility type. The previous analysis of these data presented results by ty pe of mine or factory. Results In our study, pooling all 29 Chinese work sites, lung cancer risk s howed a modest association with silica exposure. Risk did not vary after ex cluding subjects with silicosis or adjusting the risk estimates by radiolog ical staging of silicosis. Strong correlation among exposures prevented a d etailed evaluation of the role of individual exposures. However, lung cance r risk was for the most part absent when concomitant exposure to other work place lung carcinogens, such as polycyclic aromatic hydrocarbons (PAHs), ni ckel or radon-daughters, was considered The cross classification of lung ca ncer risk by categories of exposure to respirable silica and total respirab le dust did not show an independent effect of total respirable dust. Silico sis showed a modest association with lung cancer, which did not vary by sev erity of radiological staging, or by radiological evidence of disease progr ession, or by level of silica exposure. However, among silicotic subjects, lung cancer risk was significantly elevated only when exposure to cadmium a nd PAH had occurred Conclusions Our results suggest that, among silica-exposed Chinese workers, numerous occupational and non-occupational risk factors interact in a comp lex fashion to modify lung cancer risk. Future epidemiological studies on s ilica and lung cancer should incorporate detailed information on exposure t o other workplace lung carcinogens, total respirable dust, and on surface s ize and age of silica particles to understand whether and to what extent th ey affect the carcinogenic potential of silica. (C) 2001 Wiley-Liss, Inc.