Abstract PO2-13-01: Weight change in early breast cancer-based baseline body mass index and treatment

Abstract Background: Early-stage breast cancer is a common condition with significant effects on health, both as a result of treatment and underlying conditions. Breast cancer has been associated with obesity, weight gain, and diabetes. Little is known about changes in weight after breast cancer diagnoses based on baseline weight. Additionally, weight change may differ due to treatments, such as chemotherapy or hormone therapy. Methods: A retrospective study was conducted using deidentified electronic medical records data from a national health informatics provider and insurer database to identify the cohort. The cohort inclusion criteria included women with a diagnosis of breast cancer, a breast biopsy procedure, and a breast cancer surgery within a 1-year period of time from 2010-2018. Body-mass index (BMI) within 1 month of initial biopsy was collected, and weight at 6 months and 1 year after initial biopsy was used to calculate the percentage change in weight. Treatment with chemotherapy within 1 year of diagnosis and hormone therapy within 6 months was also collected. Patients were divided into standard BMI categories as well as BMI 25 vs. ≤25. ANOVA was used to compare outcomes of weight change based on BMI, chemotherapy, and hormone therapy. Linear regression was used to analyze the effects of age, BMI, chemotherapy, and hormone therapy with weight change at 1 year. Results: In 4,541 patients diagnosed with breast cancer, 3,896 patients had weight available at 6 months and 3,406 had weight available at 1 year. Mean age at diagnosis was 61.5 years (standard deviation (SD) 12.4) with mean BMI of 29.9 at baseline (SD 7.3) and weight of 79.5 kg (SD 20.2). Chemotherapy was administered in 1206 patients (26.6%) and hormone therapy in 1,644 (36.2%) with 210 (4.6%) receiving both therapies. Overall, patients lost a mean of 0.6 kg (0.5% change, SD 5.1) at 6 months and 0.6 kg at 1 year (0.4% change, SD 5.7). At one year, patients with BMI 25 gained 0.74% of body weight vs. lost 1.1% of weight in BMI 25 (p 0.001). Patients treated with chemotherapy lost 1.4% body weight vs. lost 0.23% in patients without chemotherapy (p 0.001) and patients treated with hormone therapy lost 0.12% of body weight vs. lost 1.3% without hormone therapy. A linear regression model including age, BMI, chemotherapy, and hormone therapy to explain weight change at one year was statistically significantly better than a baseline model at explaining the weight change at one year F(4,2474)=61.05. Increasing age (b=-0.125; t=-10.546; p .001; 95% CI for beta :0.14 -0.10), BMI (b=-0.178; t=-9.428; p .001; 95%CI :0.22 -0.14), and chemotherapy (b=-1.643; t=-4.645; p .001; 95% CI: 2.4 -0.95) were all significant predictors associated with weight loss at one year while hormone therapy was also a significant predictor but was associated with weight gain (b=0.846; t=2.428; p=.015; 95% CI: 0.16-1.5). Conclusions: Women with early breast cancer experienced significant changes in weight in the year after diagnosis. Women with lower BMI gained weight while those with BMI 25 lost weight. Increasing age, BMI, and treatment with chemotherapy was associated with weight loss while use of hormone therapy was associated with weight gain. Further study of weight changes after breast cancer diagnosis are appropriate to understand outcomes and mitigate effects of treatments. Table 1: Percentage weight change across BMI groups by chemotherapy use Citation Format: Martin Schoen, Deepika Gopukumar, Abhilash Akula, Kaitlin Farrell, Aimee Schad, Leslie Hinyard. Weight change in early breast cancer-based baseline body mass index and treatment abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-13-01.