Lifetime tobacco smoke exposure and breast cancer incidence

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Abstract
Purpose We analyzed data from a case–control study to assess the association between lifetime tobacco smoke exposure and breast cancer incidence. Methods Incident breast cancer cases were identified in the Massachusetts Cancer Registry and population controls were sampled from state Medicare lists and driver’s license rosters. Demographic, lifestyle, medical history, reproductive history, and passive and active smoking exposure variables were assessed by telephone interview. We defined passive and active tobacco smoke exposure categories reflective of lifetime exposure patterns, and compared breast cancer risk among these groups while adjusting for age, body mass index, menopausal status, parity, alcohol consumption, and family history of breast cancer. We also adjusted passive smoking associations for active smoking status and vice versa. Results We observed no association between ever being passively exposed to tobacco smoke and risk of incident breast cancer (adjusted OR: 1.2; 95% CI: 0.8, 1.8) nor between active smoking and breast cancer (adjusted OR for >23 pack-years compared to nonsmokers: 0.9; 95% CI: 0.7, 1.3). Null effects persisted in finer categorizations of active and passive exposure. Conclusions We observed no causal associations between active or passive tobacco smoke exposures and incident breast cancer, consistent with results from most prospective cohort studies.