opausal Hormone Therapy and Subsequent Risk of cific Invasive Breast Cancer Subtypes in the B & P ifornia Teachers Study

nloaded kground: Although it is well established that combined estrogen-progestin therapy (EPT) increases cancer risk, questions remain regarding the effect of different formulations of hormones, whether ceromen are at particularly high risk, and whether risk varies by tumor subtype. thods: We investigated hormone therapy (HT) use in relation to breast cancer risk in the California rs Study cohort; after a mean follow-up of 9.8 years, 2,857 invasive breast cancers were diagnosed. ults: Compared with women who had never used HT, women who reported 15 or more years of estherapy (ET) use had a 19% greater risk of breast cancer (95% confidence interval, 1.03-1.37), whereas n using EPT for 15 or more years had an 83% greater risk (95% confidence interval, 1.48-2.26). Breast risk was highest among women using continuous combined EPT regimens. Risks associated with EPT Tuse were increased with duration of HTuse for women with a body mass index (BMI) of <29.9 kg/m t for women with BMI of ≥30 kg/m. Elevated risks associated with EPT and ET use were confined to s that were positive for both estrogen and progesterone receptors and those that were HER2+ but were y diminished for HER2− tumors. clusions: Breast cancer risks increased with longer duration of ET and EPT use, and risks were highest ntinuous-combined EPT use. Furthermore, risks varied by BMI and tumor subtype. for co Impact: These findings underscore the need for personalized risk-benefit discussions with women contemplating HT use. Cancer Epidemiol Biomarkers Prev; 19(9); 2366–78. ©2010 AACR.