Passive smoking exposure and female breast cancer mortality

Background: Several studies have reported positive associations between env ironmental tobacco smoke (ETS) and increased risk of breast cancer. However , studies of active smoking and risk of breast cancer are equivocal and in general do not support a positive association. To try to resolve this parad ox, we examined the association between breast cancer mortality and potenti al ETS exposure from spousal smoking in an American Cancer Society prospect ive study of U,S, adult women. Methods: We assessed breast cancer death rat es in a cohort of 146 488 never-smoking, single-marriage women who were can cer free at enrollment in 1982, Breast cancer death rates among women whose husbands smoked were compared with those among women married to men who ha d never smoked. Cox proportional hazards modeling was used to control for p otential risk factors other than ETS exposure. Results: After 12 years of f ollow-up, 669 cases of fatal breast cancer were observed in the cohort. Ove rall, we saw no association between exposure to ETS and death from breast c ancer (rate ratio [RR] = 1.0; 95% confidence interval [CI] = 0.8-1.2). We d id, however, find a small, not statistically significant increased risk of breast cancer mortality among women who were married before age 20 years to smokers (RR = 1.2; 95% CI = 0.8-1,8). Conclusions: In contrast to the resu lts of previous studies, this study found no association between exposure t o ETS and female breast cancer mortality. The results of our study are part icularly compelling because of its prospective design as compared with most earlier studies, the relatively large number of exposed women with breast cancer deaths, and the reporting of exposure by the spouse rather than by p roxy.