Evaluation of cardiotoxicity following breast cancer irradiation in an Asian cohort in real-world settings

BACKGROUND: Adjuvant radiotherapy (RT) for early-stage breast cancer is associated with increased major cardiovascular (CV) events. This study investigates cardiac toxicity in an Asian breast cancer cohort, focusing on the interplay between RT, cardiovascular risk factors, and systemic treatments, a topic less explored in regions with lower cardiovascular disease (CVD) prevalence. METHODS: Patients with breast cancer who underwent adjuvant RT between January 2004 and November 2014 were included in this single-institutional retrospective study. Patients were categorized by CVD risk factors, including obesity, smoking history, prior CVD incidents, chronic kidney disease (CKD), diabetes mellitus, hypertension, and dyslipidemia. The primary outcome was the incidence of major CV events, defined as conditions requiring intervention, including heart failure, arrhythmia, and ischemic heart disease. Kaplan-Meier methods, log-rank tests, and Cox regression models were used for statistical analysis. RESULTS: Among the 975 patients, the 10-year cumulative incidence of major CV events was 3.7 %, with no significant difference (p = 0.892) between right-sided (3.8 %) and left-sided RT (3.4 %). Patients with low, intermediate, and high CVD risk factors had 10-year cumulative incidences of 0.7 %, 2.5 %, and 13.7 %, respectively. Multivariate analysis revealed that hypertension, CKD, and previous CVD were significantly associated with major CV events. In patients without CVD risk factors, the 10-year incidence of CV events was higher in those undergoing left-sided RT compared to right-sided RT (1.3 % vs. 0.0 %, p = 0.032). CONCLUSIONS: Major CV events incidences following RT in this Asian cohort with low baseline CVD risk were modest. However, the impact was more pronounced in patients without baseline CVD risk factors, emphasizing the need for personalized risk assessment in RT planning.