Abstract PD12-01: PD12-01 Impact of obesity and post-diagnosis weight change on survival in women with breast cancer diagnosed at Smilow Cancer Hospital from 2013-2019

Abstract Background: The association between obesity and breast cancer risk is well documented, but fewer studies have explored the impact of post diagnosis weight changes on survival especially in more contemporary contexts. The existing evidence has mainly focused on weight gain, been limited by small sample sizes and has evaluated prospective cohorts with restrictive eligibility criteria rather than population-based samples. Our study uniquely contributes to the literature by using a population-based approach and recent clinically measured weight data from the electronic health record (EHR) to explore the impact of weight change following a breast cancer diagnosis on survival. Methods: EHR weight measurements were extracted for women diagnosed with stages I-IV breast cancer at CT’s Smilow Cancer Hospital and Care Network between 2013-2019 (N=6,934). During the follow-up period through April 26, 2020 (mean=3.2 years, standard deviation=1.8), there were 497 deaths. We used multivariable Cox regression models, adjusting for age at diagnosis, race/ethnicity, chemotherapy, radiation therapy, ER/PR subtype, to estimate the association between body mass index (BMI) at diagnosis and all-cause mortality from time since first post-diagnosis clinic visit (within 6 months of diagnosis). Percent weight change at 1-year post-diagnosis was categorized as a 5-level variable (weight stable – change within 5% of weight at diagnosis, moderate weight loss – 5% to < 10% change, large weight loss – ≥10% change, moderate weight gain – 5% to < 10% change, and large weight gain – ≥10% change) and evaluated in relation to all-cause mortality. A non-linear relationship between percent weight change at 1-year post-diagnosis and mortality was evaluated by comparing linear and cubic spline models. Results: Among these 6,934 breast cancer cases, the mean age was 61±13 years, BMI at diagnosis was 29±7 kg/m2 and weight change from diagnosis to 1-year post-diagnosis was -0.47±5.4 kg. Being underweight (BMI< 18.5) or having class II obesity (BMI>35) at diagnosis were statistically significantly independently associated with higher all-cause mortality compared with normal BMI (Hazard Ratio [HR]=1.43, 95% Confidence Interval [CI]=1.11-1.85 and HR=3.32, 95% CI=1.90-5.80, respectively). At 1-year post-diagnosis, 64% of women remained weight stable since diagnosis, 12% gained moderate body weight, 5% had large weight gain, 12% lost moderate weight and 7% experienced a large weight loss. Compared with the weight stable group, there was a positive, non-significant association between moderate weight gain at 1-year post-diagnosis and overall mortality (HR=1.24, 95% CI=0.84-1.81). Greater than 10% weight loss at 1-year post-diagnosis was statistically significantly associated with higher mortality (HR=2.87, 95% CI=2.13-3.87). The test for curvature suggested a non-linear relationship between percent weight change at 1-year and mortality (p< 0.001). Conclusion: In this contemporary, population-based study of women with breast cancer from one large academic medical center, underweight and obesity at diagnosis were associated with poorer survival. Weight loss during the first-year post-diagnosis was also strongly associated with an increased risk of mortality. To further inform weight management strategies and future interventions for breast cancer survivors, we need to better understand changes in body composition in the post-diagnosis period. Citation Format: Leah Puklin, Fangyong Li, Brenda Cartmel, Tara B. Sanft, Alexa Lisevick, Eric Winer, Maryam Lustberg, Mona Sharifi, Melinda L. Irwin, Leah Ferrucci. PD12-01 Impact of obesity and post-diagnosis weight change on survival in women with breast cancer diagnosed at Smilow Cancer Hospital from 2013-2019 [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD12-01.