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

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.

Data from a multi-center, population-based, case-control study among women under age 55 were analyzed.

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 < or = 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.

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.