A population-based case-control study of breast cancer and active smoking and environmental tobacco smoke among postmenopausal women in Montreal, Canada /

This population-based multi-centered case-control study of incident postmenopausal breast cancer was carried out in Montreal. Case subjects included all incident histologically confirmed breast cancer among postmenopausal women, age 51--75 years, diagnosed in 1996 and 1997 in all major hospitals. Control subjects had other histologically-confirmed sites of cancer from the same hospital, and were approximately frequency-matched by age to the case subjects. Detailed information was obtained on active smoking and exposure to environmental tobacco smoke (ETS) in the home before the age of 18 and in the workplace as an adult. Unconditional logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (CI) between the risk of postmenopausal breast cancer and various indices of smoking and exposure to ETS. The OR for breast cancer among women with exposure to active smoking only was 0.71 (9596 CI: 0.34--1.48), for early exposure to ETS only, the OR was 1.09 (95% CI: 0.65--1.85), and for occupational exposure to ETS only, the OR was 1.00 (95% CI: 0.53--1.90). When occupational and early exposures to ETS were combined, the OR was 1.40 (95% CI: 0.81--2.40). In summary, I found no associations between the incidence of postmenopausal breast cancer and active smoking or exposure to ETS