RMTC-07 OBESITY AND RISK OF BRAIN METASTASES AMONG PATIENTS DIAGNOSED WITH EARLY-STAGE BREAST CANCER: A POPULATION-BASED COHORT STUDY
Abstract Background Obesity is characterized by chronic low-grade systemic inflammation and altered metabolic signaling, which may disrupt periphery-to-brain communication and compromise central nervous system interfaces. These obesity-associated inflammatory perturbations may influence tumor seeding and the phenotypic presentation of brain metastases (BrM). Methods We conducted a retrospective, population-based cohort study using linked administrative health data from ICES (Ontario, Canada). Women aged ≥18 years diagnosed with stage I–III breast cancer (2009–2021) were followed through 2023. Baseline obesity was defined using validated administrative codes. The primary outcome was incident BrM. Time-to-event analyses were performed with death as a competing risk. Cumulative incidence functions were compared using Gray’s test and Fine–Gray sub-distribution hazard models were used for survival analyses. Results Among 92,973 patients, 3,195 (3.4%) had obesity, defined using validated administrative coding. Median age was 61 years (IQR 51–71), and stage distribution was 53.5%, 33.7%, and 12.8% for stage I, II, and III disease, respectively. With a median follow-up of 6.9 years (IQR 4.1–10.3), 2,037 BrM events and 14,937 competing deaths occurred. BrM incidence rates were similar between obese and non-obese groups (2.7 vs 3.0 per 1,000 person-years; p = 0.31). Neither the cumulative incidence of BrM (Gray’s p = 0.32) nor the cumulative incidence of death (Gray’s p = 0.99) differed significantly between groups. In a subset of patients with BMI data (∼40%), a statistically significant association between increasing BMI and shorter time-to-development of BrM was observed when BMI was modeled as a continuous variable (HR 1.044 per 10-unit increase, 95% CI 1.027–1.061). Conclusions In this large population-based cohort, baseline obesity was not associated with risk of BrM. However, BMI when measured as a continuous variable, was associated with a significantly shorter time-to-development of BrM, a finding that warrants further study.