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

Objectives: To evaluate whether heavy cigarette smoking as a teenager or lo ng-term smoking increases breast cancer risk or, alternatively, whether smo king acts as an anti-estrogen and reduces risk. Methods: Data from a multi-center, population-based, case-control study amo ng women under age 55 were analyzed. Results: Among women under age 45, there was at modest inverse relation wit h 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 b egan at an early age (0.59 for less than or equal to 15, 95% CI = 0.41, 0.8 5) 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 curr ent 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 = 0.3 4, 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 wit h smoking. Conclusions: These results suggest that breast cancer risk among women unde r 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.