Effect of change of body mass index (BMI) during therapy on the efficacy of endocrine therapy in premenopausal patients with breast cancer: An analysis of the ABCSG-12 trial.

514 Background: Aromatase inhibitors (AIs) are effective as adjuvant endocrine treatment in breast cancer (BC) patients. Recently, it has been argued that BMI at BC diagnosis impacts on the efficacy of endocrine therapy. Interventional trials try to identify a benefit on outcome by BMI change after BC diagnosis. As endocrine therapy may lead to an increase of body weight, we investigated the impact of BMI change during therapy on BC outcome. Methods: ABCSG-12 examined the efficacy of ovarian suppression using goserelin (3.6 mg q28d SC) in combination with anastrozole (ANA) or tamoxifen (TAM) ± zoledronic acid (ZOL 4 mg IV q6mo) in premenopausal women with endocrine-responsive BC. BMI was calculated using prospectively collected data on weight and height at study entry as well as every three months up to 3 years of endocrine treatment. Comparisons between BMI at study entry and BMI during therapy were done by Wilcoxon signed rank test. Comparisons of BMI changes between ANA and TAM were done by Kruskal-Wal...