Cigarette smoking and breast cancer risk among young women (United States)

Objectives: To evaluate whether heavy cigarette smoking as a teenager or long-term smoking increases breast cancer risk or, alternatively, whether smoking acts as an anti-estrogen and reduces risk. Methods: Data from a multi-center, population-based, case-control study among women under age 55 were analyzed. Results: Among women under age 45, there was a modest inverse relation with current (OR = 0.82, 95% CI = 0.67, 1.01) but not past (OR = 0.99, 95% CI = 0.81, 1.21) smoking. Odds ratios were decreased for current smokers who began at an early age (0.59 for ≤ 15, 95% CI = 0.41, 0.85) or continued for long periods of time (0.70 for > 21 years, 95% CI = 0.52, 0.94), In subgroup analyses, reduced odds ratios were observed among current smokers who were ever users of oral contraceptives (0.79, 95% CI = 0.63, 0.98), were in the lowest quartile of adult body size (0.53, 95% CI = 0.34, 0.81), or never or infrequently drank alcohol (0.68, 95% CI = 0.47, 0.98). Among women ages 45-54, there was little evidence for an association with smoking. Conclusions: These results suggest that breast cancer risk among women under age 45 may be reduced among current smokers who began smoking at an early age, or long-term smokers, but require confirmation from other studies.