Impact of Body Mass Index on the Efficacy of Endocrine Therapy in Premenopausal Patients With Breast Cancer: An Analysis of the Prospective ABCSG-12 Trial

Purpose Aromatase inhibitors are effective as endocrine treatment for patients with hormone receptor–positive breast cancer. According to the hypothesis that overweight patients have higher levels of aromatase enzyme availability, we investigated the influence of body mass index (BMI) on the efficacy of adjuvant endocrine therapy in premenopausal patients in a retrospective analysis of the Austrian Breast and Colorectal Cancer Study Group (ABCSG) 12 trial. Patients and Methods ABCSG-12 examined the efficacy of ovarian suppression using goserelin (3.6 mg subcutaneously every 28 days) in combination with anastrozole or tamoxifen with or without zoledronic acid (4 mg intravenously every 6 months) in premenopausal women with endocrine-responsive breast cancer. BMI was calculated using the prospectively collected data on patients' height and weight at study entry. BMI categories have been differentiated according to the WHO definition. Results Overweight patients treated with anastrozole had a 60% increase in the risk of disease recurrence (hazard ratio [HR], 1.60; 95% CI, 1.06 to 2.41; P = .02) and more than a doubling in the risk of death (HR, 2.14; 95% CI, 1.17 to 3.92; P = .01) compared with normal weight patients treated with anastrozole. In the overweight group, patients treated with anastrozole had a nearly 50% increase in the risk of disease recurrence (HR, 1.49; 95% CI, 0.93 to 2.38; P = .08) and a three-fold increase in the risk of death (HR, 3.03; 95% CI, 1.35 to 6.82; P = .004) compared with patients treated with tamoxifen. Conclusion BMI significantly impacts on the efficacy of anastrozole plus goserelin in premenopausal patients with breast cancer, probably through influencing aromatase availability and/or ovarian suppression by goserelin.