Weight trajectories during first two years of endocrine treatment: Premenopausal compared to postmenopausal early breast cancer survivors

e12069 Background: Obesity and weight gain in breast cancer survivors (BCS) can impact prognosis, survival, and quality of life. Women who were premenopausal (PreBCS) or postmenopausal (PostBCS) at BC diagnosis are compared regarding weight change during the first 2 years of endocrine treatment (ET) and factors associated with > 2kg weight gain. Methods: Data were gathered by retrospective chart review, with weights assessed by nursing staff during routine clinic visits. Chi-squared and t-tests were used to compare PostBCS and PreBCS characteristics, and log-binomial regression models to evaluate factors associated with > 2kg weight gain. Results: In a final sample of N = 447 BCS, 33% were PreBCS (mean age 44) and 67% were PostBCS (mean age 65). PreBCS had lower BMI at diagnosis (p = 0.003), lower proportion of white (p = 0.04), fewer comorbidities (p < 0.0001); higher stage (p < 0.0001), grade (p = 0.008), node positive (p < 0.0001), PR positive (p = 0.03), and HER2 positive (p = 0.03) BC tumors; higher proportion of mastectomies (p < 0.0001), axillary node dissection (p = 0.005), chemotherapy (p < 0.0001), radiation treatment (p = 0.009), and Tamoxifen use (p < 0.0001); and less weight loss between diagnosis and start of ET (p = 0.013). After 2 years of ET, 48% of PreBCS and 39% of PostBCS had gained > 2kg (p = 0.08). In univariate analysis, factors associated with > 2kg weight gain were: weight loss between BC diagnosis and ET start (p < .0001), lower age at start of ET (p = .002), higher tumor size (p = .003), increasing stage (p < .0001), mastectomy (p = .0002), axillary node dissection (p = .005), positive nodal status (p = 0.0003), and chemotherapy (p < .0001). In multivariable analysis controlling for covariates that differed between PreBCS/PostBCS, only weight change between BC diagnosis and ET start was associated with > 2kg weight gain (p = 0.0005). Conclusions: In our sample, neither menopausal status nor type of ET was significantly associated with weight gain during ET. Our research suggests that BC survivors with higher risk tumors and associated treatments may experience higher weight gain during ET and warrant weight management counseling.