Body mass index as an independent risk factor for cancer therapy-related cardiac dysfunction: a retrospective cohort study in breast cancer patients

Background: Obesity is a known cardiovascular risk factor, yet its role in predicting chemotherapy-induced cardiotoxicity remains unclear. This study aimed to evaluate body mass index (BMI) as an independent risk factor for cancer therapy–related cardiac dysfunction (CTRCD). Methods: We conducted a retrospective cohort study involving 133 patients with human epidermal growth factor receptor 2-positive breast cancer treated with trastuzumab between 2022 and 2025. After excluding individuals with major cardiovascular comorbidities, 65 patients who developed CTRCD were matched with 68 controls who completed therapy without cardiotoxicity. CTRCD was defined according to the European Society of Cardiology using echocardiographic and biomarker assessments. BMI was categorized according to the World Health Organization, and its association with CTRCD risk and severity was analyzed. Results: No statistically significant difference in baseline BMI was observed between the CTRCD (29.6 ± 7.6) and control (30.5 ± 10.2; P = 0.62) groups, suggesting that BMI alone does not independently predict the development of CTRCD. However, in the CTRCD group, patients with moderate/severe dysfunction had significantly higher BMIs than those with mild CTRCD (32.1 ± 8.2 vs. 28.9 ± 6.8; P = 0.04). A trend suggesting a synergistic interaction between obesity and anthracycline use was observed ( P = 0.08). Conclusion: BMI was not an independent predictor of CTRCD occurrence in this cohort, but a higher BMI was associated with increased severity of cardiotoxicity. Our findings suggest that traditional definitions of obesity based solely on BMI may not adequately reflect cardiometabolic risk in cancer patients. Future studies should focus on fat distribution and metabolic health markers.