Lung cancer among tin miners in southeast China: silica exposure, silicosis, and cigarette smoking.

The Dachang Tin Mine is an industrial facility with high rates of lung cancer compared to the resident population in Guangxi province in southern China. Historically, exposure to silica dust was very high in the 1950s, falling in recent years to levels in keeping with international standards. Radon levels in the mine are low. We report the findings of a case-control study nested into a cohort study on miners working in Dachang. Cases of lung cancer among miners incident from 1973-1989 were obtained from local comprehensive medical records covering workers employed at the mine. These were matched approximately 3 to 1 with miners randomly chosen from the district surrounding the mine within the same birth decade. Matched odds ratios of 2.42 (95% confidence limit [CL] 1.3, 4.4) for underground employment, 3.52 (95% CL 1.7, 7.5) for smoking, and 2.04 (95%) CL 1.2, 3.7) for silicosis as determined on chest film were noted. Multifactor analysis of unconditional logistic regression showed that among the risk factors for excess mortality from lung cancer only the years spent drilling underground and the cumulative smoking index (product of daily cigarette consumption and number of years smoking) were independent contributors to risk and there was no interaction observed. The presence of silicosis did not contribute to predicting risk independently of the years spent underground.