Silica and cancer associations from a multicancer occupational exposure case-referent study

A multicancer site, multifactor case-control study was undertaken to generate hypotheses about possible occupational carcinogens. Eligible cases, comprising all incident cases of cancer at 14 sites who were male, aged 35-70 and resident in Montreal, were subjected to probing interviews designed to obtain detailed lifetime job histories and information on potential confounders. Each job history was reviewed by a team of chemists who translated it into a history of occupational exposures. These occupational exposures were then analysed as potential risk factors in relation to the sites of cancer included. Over 3700 cases were interviewed and processed. For each site of cancer analysed as a case series, controls were selected from subjects with cancer at the other sites covered in the study. This report concerns the associations between silica exposure and each site of cancer. In initial screening analyses, there were significantly elevated odds ratios for silica and stomach cancer and for silica and non-adenocarcinoma lung cancer. More detailed analyses confirmed these associations, though there was no evidence of a dose-response relationship for stomach cancer. For lung cancer, there were significantly elevated risks in those with high-level long-term exposure. These results, which took into account several potential confounders including cigarette smoking and asbestos exposure, lend credence to the hypothesis that silica exposure increases the risk of lung cancer, and suggest the possibility of an effect on stomach cancer.