Retrospective cohort study of laterality of breast radiotherapy and ischemic heart disease by cardiovascular risk burden

Although modern radiotherapy (RT) techniques have reduced cardiac exposure, concerns regarding breast RT-induced heart disease persist. Identifying which patients are most vulnerable to cardiac toxic effects is crucial for personalized survivorship care. A retrospective nationwide cohort study using data on 23 305 women in the Korean National Health Insurance Service database evaluated whether the association between tumor laterality and ischemic heart disease (IHD) varies by cumulative baseline cardiovascular risk burden (defined as a count of 6 factors: age ≥ 55 years, obesity, smoking, hypertension, diabetes, and dyslipidemia). A total of 11 723 (50.3%) patients received left-sided RT and 11 582 (49.7%) received right-sided RT. Left-sided RT was associated with a statistically significant increase in IHD risk (sHR 1.11; p=0.04). No statistically significant difference in IHD risk between left- and right-sided RT was observed among patients with 0-2 cardiovascular risk factors, whereas left-sided RT was associated with significantly higher IHD risk among patients with 3 risk factors (sHR 1.37; p=0.004). The authors conclude that these findings suggest that among patients with low baseline risk profiles, the difference in IHD risk between left- and right-sided treatment may be small, whereas those with high cardiovascular burden warrant prioritized access to advanced heart-sparing modalities and aggressive risk factor management.