Passive smoking at home and cancer risk: a population-based prospective study in Japanese nonsmoking women

Objectives: To investigate the relationship between passive smoking at home and the incidence of various cancers in a population-based prospective stu dy. Methods: The subjects were 9675 Japanese lifelong nonsmoking women aged ove r 40 years who lived in three municipalities of Miyagi Prefecture, and comp leted a self-administration questionnaire in 1984. During 9 years of follow -up, 426 cancers were identified by record linkage to the population-based cancer registry. The data were analyzed using the Cox proportional hazards model. Results: The age-adjusted relative risks (RR) and 95% confidence intervals (CI) of smoking-related cancers and lung cancer for women who had smoking h usbands, compared with women whose husbands did not smoke, were 1.7 (0.94-2 .9, p = 0.079) and 1.9 (0.81-4.4, p = 0.14), respectively. In contrast, a s ignificant inverse association was observed for breast cancer; the RR (95% CI) was 0.58 (0.34-0.99, p = 0.047). After multivariate adjustment for conf ounding factors, the risks of smoking-related cancers and breast cancer wer e materially unchanged. Conclusions: These results show that passive smoking may affect the risk of cancers other than lung cancer.