Obesity, Tamoxifen Use, and Outcomes in Women With Estrogen Receptor–Positive Early-Stage Breast Cancer

breast cancer risk and poorer prognosis after disease onset. However, little is known about the effect of obesity on treat-ment efficacy. We evaluated the association of obesity with outcomes and with tamoxifen efficacy in women with early-stage, hormone-responsive breast cancer participating in a multicenter cancer cooperative group clinical trial. Methods: The cohort consisted of 3385 women enrolled in National Surgical Adjuvant Breast and Bowel Project (NSABP) pro-tocol B-14, a randomized, placebo-controlled trial evaluating tamoxifen for lymph node–negative, estrogen receptor (ER)– positive breast cancer. Hazards of breast cancer recurrence, contralateral breast tumors, other new primary cancers, and several mortality endpoints were evaluated in relation to body mass index (BMI), using statistical modeling to adjust for other prognostic factors. Median follow-up time was 16