Active and passive smoking, IL6, ESR1, and breast cancer risk

We evaluated the association between smoking and risk of breast cancer in non-Hispanic white (NHW) and Hispanic or American Indian (HAI) women living in the Southwestern United States. Data on lifetime exposure to active and passive smoke data were available from 1527 NHW cases and 1601 NHW controls; 798 HAI cases and 924 HAI controls. Interleukin 6 (IL6) and Estrogen Receptor alpha (ESR1) polymorphisms were assessed in conjunction with smoking. Pack-years of smoking (≥15) were associated with increased risk of pre-menopausal breast cancer among NHW women (OR 1.6, 95% CI 1.1–2. 4). Passive smoke increased risk of pre-menopausal breast cancer for HAI women (OR 1.9, 95% CI 1.1–3.1 everyone; OR 2.3, 95% CI 1.2–4.5 nonsmokers). HAI pre-menopausal women who were exposed to 10+ h of passive smoke per week and had the rs2069832 IL6 GG genotype had over a fourfold increased risk of breast cancer (OR 4.4, 95% CI 1.5–12.8; P for interaction 0.01). Those with the ESR1 Xba1 AA genotype had a threefold increased risk of breast cancer if they smoked ≥15 pack-years relative to non-smokers (P interaction 0.01). These data suggest that breast cancer risk is associated with active and passive smoking.