Abstract 3425: Genetic predisposition to obesity and survival in women with breast cancer

Abstract Background. Higher body mass index (BMI) is associated with poor survival after breast cancer diagnosis. BMI is a heritable trait. A polygenic risk score (PRS) for BMI has been associated with cardiometabolic traits and found to modify weight loss interventions. Whether BMI genetic scores affect survival in women with breast cancer is unknown. Methods. This analysis was conducted in the Cancer Prevention Study II Nutrition cohort. Women diagnosed with non-metastatic breast cancer between 1992 and 2017 were included in the analysis if they had genotype data. Analyses were restricted to unrelated, postmenopausal women at the time of diagnosis who were of European ancestry (N=3,566). Deaths through 2020 were identified through linkage with the National Death Index. Primary cause of death was based on the International Classification of Disease codes. Pre-diagnosis BMI was self-reported (median 1.3 years from BMI measurement to diagnosis, interquartile range (IQR): 0.6, 1.9). We constructed a PRS using findings from a published meta-analysis of BMI genome wide association studies (GWAS) that included ~700,000 individuals and the PRSice tool.Hazard ratios (HR) and 95% confidence intervals (CI) between the PRS and all-cause mortality were estimated using Cox proportional hazards regression and Fine and Gray models for cause-specific mortality to account for competing risks. Models were adjusted for age and GWAS-specific statistically significant (P<0.05) principal components for population stratification. Mediation was estimated using the mediation R package. Results. The median age at diagnosis was 71.5 years (IQR: 66.3, 76.8). Most women were overweight (33.5%) or obese (18.4%) and were diagnosed with localized stage (63%) and estrogen receptor positive (65%) breast cancer. During a median follow-up of 14.5 years (IQR: 9.7-19.8), there were 1,825 (51.2%) deaths, including 301 breast cancer and 337 cardiovascular disease (CVD) specific deaths. In multivariable models, a 5 Kg/m2 increase in BMI was associated with increased risks of all-cause mortality (HR=1.09, 95% CI: 1.04, 1.15), breast cancer-specific mortality (HR=1.27, 95% CI: 1.13, 1.42), and CVD-specific mortality (HR=1.25, 95% CI: 1.11, 1.41). The PRS was highly predictive of pre-diagnostic BMI (P<0.001). A 1-standard deviation increase in the PRS was associated with statistically increased risk of all-cause mortality (HR=1.06, 95% CI: 1.02, 1.11). Risks of breast cancer (HR=1.07, 95% CI: 0.96, 1.19) or CVD (HR=1.01, 95% CI: 0.90, 1.12) specific mortality did not reach statistical significance. We estimated that 27% of the PRS and all-cause mortality association was mediated by BMI (95% CI: 12%, 91%; P=0.004). Conclusions. Women with breast cancer predisposed to higher BMI were at increased risk of all-cause mortality. A BMI-related PRS may be a useful tool to identify women with breast cancer in need of additional interventions and/or surveillance. Citation Format: Clara Bodelon, Adriana Lori, Mariah Landry, James Hodge, Parichoy Pal Choudhury, Ying Wang, Lauren E. McCullough, Alpa V. Patel, Lauren R. Teras. Genetic predisposition to obesity and survival in women with breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3425.