Associations of race and obesity with mortality and cardiotoxicity in breast cancer.

e23304 Background: Racial disparities in mortality and cardiotoxicity among breast cancer patients remain insufficiently characterized. Prior studies have shown limited variation in overall cardiotoxicity, but the extent to which race and obesity independently influence specific cardiotoxic endpoints is still unclear. To address this gap, we evaluated the associations of race and obesity with mortality and cardiotoxicity outcomes in a large, diverse breast cancer cohort. Methods: We conducted a retrospective cohort study of 31,312 breast cancer patients diagnosed within Kaiser Permanente Southern California between 2007 and 2022. Mortality outcomes included all-cause, cancer-specific, and cardiovascular disease (CVD) mortality. Cardiotoxicity outcomes included congestive heart failure (CHF), cardiomyopathy, and major adverse cardiovascular events (MACE), with Percutaneous Transluminal Coronary Angioplasty and Coronary Artery Bypass Grafting procedures included. Associations of race and obesity with these outcomes were evaluated using Cox proportional hazards models adjusted for age, smoking status, tumor stage and grade, laterality, insurance type, and pre-existing cardiovascular comorbidities. Results: Asian (HR 0.66, 95% CI 0.59–0.73) and Hispanic patients (HR 0.85, 0.78–0.92) had lower all-cause mortality than Non-Hispanic White (NHW) patients, while underweight status increased risk (HR 2.06, 1.62–2.62) and overweight/Class I–II obesity had lower hazard. For cancer-specific mortality, Non-Hispanic Black (NHB) patients had higher risk (HR 1.21, 1.07–1.37), whereas Asian (HR 0.57, 0.49–0.68) and Hispanic patients (HR 0.80, 0.71–0.89) had lower risk. Asian (HR 0.52, 0.43–0.63) and Hispanic patients (HR 0.70, 0.62–0.80) also had lower CVD mortality. No racial differences were observed in CHF, but obesity showed a strong graded association, with Class III obesity conferring the highest CHF risk (HR 1.82, 1.51–2.20). For cardiomyopathy, NHB patients had higher risk (HR 1.40, 1.18–1.67) and Asian patients’ lower risk (HR 0.73, 0.58–0.93); obesity was not associated with cardiomyopathy. For MACE with procedures, Asian (HR 0.67, 0.61–0.74) and Hispanic patients (HR 0.86, 0.79–0.92) had lower hazards. Underweight status increased MACE risk (HR 2.03, 1.62–2.53), while overweight and Class I–II obesity had lower hazard (HRs 0.82–0.88). Conclusions: Mortality and cardiotoxicity risks vary meaningfully by race and body weight. NHB patients had higher cardiomyopathy and cancer-specific mortality, while Asian and Hispanic patients consistently demonstrated lower MACE and mortality risks. Clinicians should incorporate race-aware and weight-stratified risk assessment into survivorship care, with heightened vigilance for cardiomyopathy in Non-Hispanic Black patients and for CHF in patients with severe obesity.