Economic status, smoking, occupational exposure to rubber, and lung cancer: a case-cohort study

Recent studies tend consistently to confirm the presence of a moderate excess risk of lung cancer in the rubber industry. However, the agent responsible for the excess of lung cancer is still obscure. Also, analyses without regard to the modifying effects of sex, economic status, and smoking habit are less than satisfactory. To explore these questions, we have conducted a case-cohort study using the data of 51 lung cancer deaths in 1973-1997 and a random sample (sub-cohort) of 188 from among 1598 subjects in a rubber factory in Shanghai, China. We computed the risks of lung cancer by economic status, smoking habit, coal fumes in home, and year of first employment. We assessed lung cancer risks for occupational exposures, unadjusted and adjusted for economic status and smoking. After confounding effects of smoking and economic status were controlled, we found that rate ratios were 1.43 (95% confidence interval (CI) 0.43-4.69), 1.79 (95% CI 0.64-5.03), and 3.76 (95% CI 1.44-9.86) for 1-14, 15-29, and 30-45 exposure-years in curing department, respectively. The data showed significant trends in increased risk of lung cancer with duration of exposure in tire-curing department (score test for trend:, P = 0.004). However, in front rubber processing (weighing and mixing, calendering, extruding, and milling), no significant excess risk of lung cancer was found. If it can be confirmed that nitrosamines are mainly generated in back rubber processing (curing and vulcanizing), it would be reasonable to conclude that excess risk of lung cancer in rubber industry is attributable, at least partially, to exposure to nitrosamines.