The 13th World Conference on Tobacco OR Health

Objective: To examine the risk of breast cancer associated with passive and active smoking and to explore risk heterogeneity between studies.

Methods: Nineteen of 20 located published studies of passive smoking and breast cancer risk among women met basic quality criteria. Pooled risks for breast cancer were calculated for: 1) life-long non-smokers with regular passive exposure to tobacco smoke; and 2) women who smoked. They were compared to women who were never regularly exposed to tobacco smoke.

Results: The pooled risk estimate for breast cancer associated with passive smoking among life-long non-smokers was 1.27 (95% confidence interval (CI), 1.11-1.45). In the subset of 5 studies (all case-control studies) with more complete exposure assessment (quantitative long-term information on the three major sources of passive smoke exposure: childhood, adult residential and occupational), the pooled risk estimate for exposed non-smokers was 1.90 (95%CI, 1.53-2.37). Increased risk was observed in 3 of 4 Asian cohort studies.

The overall premenopausal breast cancer risk associated with passive smoking among lifelong non-smokers was 1.68 (95%CI 1.33-2.12), and 2.19 (95% CI 1.68-2.84) for the 5 of 14 studies with more complete exposure assessment.

For women who had smoked the breast cancer risk estimate was 1.43 (95%CI 1.12-1.80) when compared to women with neither active nor regular passive smoke exposure; 1.98 (95% CI 1.40- 2.81) for more complete and 1.15 (95% CI 0.92-1.43) for less complete passive exposure assessment. Studies with thorough passive smoking exposure assessment implicate passive and active smoking as risk factors for premenopausal breast cancer.