Purpose: Active smoking and passive smoking have been associated with increased risk of breast cancer. The purpose of the present study was to prospectively assess associations of smoking with breast cancer and identify subgroups at higher risk among African-American women.
Methods: Based on 1,377 incident cases identified during 14 years of follow-up in the Black Women's Health Study, we assessed active and passive smoking in relation to breast cancer incidence by menopausal status, estrogen receptor status, and other factors. Incidence rate ratios (IRR) and 95 % confidence intervals (CI) for categories of smoking relative to no active or passive smoking were calculated from Cox proportional hazards models, controlling for breast cancer risk factors.
Results: Active smoking was associated with increased risk of premenopausal breast cancer. The IRR was 1.21 (95 % CI 0.90-1.62) for premenopausal breast cancer overall and 1.70 (95 % CI 1.05-2.75) for premenopausal breast cancer associated with beginning smoking before age 18 together with accumulation of ≥20 pack years. The positive association with premenopausal breast cancer was most apparent for estrogen-receptor-positive cancer. Passive smoking was also associated with increased risk of premenopausal breast cancer (IRR = 1.42, 95 % CI 1.09-1.85), based on information on passive smoking at home and work. Neither active nor passive smoking was associated with increased risk of postmenopausal breast cancer.
Conclusion: These results strengthen the evidence that both active and passive smoking increase the incidence of premenopausal breast cancer.