Key result
Left-sided breast radiotherapy is linked to ~11% higher IHD risk vs. right-sided treatment.
Why the study?
Although modern radiotherapy techniques reduce cardiac exposure, concerns regarding radiotherapy-induced heart disease persist, requiring identification of patients most vulnerable to cardiac toxic effects.
Does left-sided postoperative breast radiotherapy increase the risk of incident ischemic heart disease compared to right-sided radiotherapy in women with varying baseline cardiovascular risk burdens?
Cohort (n=23,305)
Yes
Does left-sided postoperative breast radiotherapy increase the risk of incident ischemic heart disease compared to right-sided radiotherapy in women with varying baseline cardiovascular risk burdens?
Left-sided breast radiotherapy increases the risk of ischemic heart disease primarily in patients with a high baseline cardiovascular risk burden, highlighting the need for risk-stratified cardiac-sparing techniques.
Answers are grounded in this paper and cite their sources.
Captured external expert commentary on this paper, strongest first. Original sources are linked where available.
“This large national cohort study by Chung and Noh reinforces the notion that laterality remains a significant factor in the cardiotoxicity of breast radiotherapy, but its impact is not uniform across all patients. While the overall absolute risk difference between left-sided and right-sided radiotherapy was modest, the risk became more pronounced in patients with a higher burden of cardiovascular risk factors. This highlights the need for a more personalized approach to cardiac risk assessment and mitigation in patients undergoing breast radiotherapy.”
“These patterns reinforce a multiple-hit model in which modest radiotherapy-related injury becomes clinically meaningful when layered on systemic therapy effects and a longer survivorship horizon”
“Cardio-oncology guidance emphasizes baseline risk assessment, targeted surveillance, and aggressive management of modifiable risk factors tailored to treatment exposures and vulnerability. For many survivors, the highest-yield intervention is systematic prevention: blood pressure and lipid control, diabetes optimization, smoking cessation, and physical activity.”
Left-sided radiotherapy was associated with excess ischemic heart disease risk mainly in patients with ≥3 cardiovascular risk factors; extends laterality data but leaves open prospective validation.
Importance Although modern radiotherapy (RT) techniques have reduced cardiac exposure, concerns regarding RT-induced heart disease persist. Identifying which patients are most vulnerable to cardiac toxic effects is crucial for personalized survivorship care. Objective To evaluate whether the association between tumor laterality and ischemic heart disease (IHD) risk varies by cumulative baseline cardiovascular risk burden. Design, Setting, and Participants This retrospective nationwide cohort study used data on 23 305 women in the Korean National Health Insurance Service database who underwent postoperative RT for breast cancer without prior IHD from January 1, 2002, to December 31, 2018. The median follow-up was 4.3 years (IQR, 2.5-6.5 years); data analysis was completed in March 2023. Exposures Treatment laterality (left-sided vs right-sided RT) and baseline cardiovascular risk burden (defined as a count of 6 factors: age ≥55 years, obesity, smoking, hypertension, diabetes, and dyslipidemia). Main Outcomes and Measures The cumulative incidence of IHD was estimated using competing-risk analysis. Subdistribution hazard ratios (sHRs) were calculated using Fine-Gray models. Results Of 23 305 patients (mean [SD] age, 51.7 [9.2] years), 11 723 (50.3%) 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; 95% CI, 1.01-1.22; P = .04). No statistically significant difference in IHD risk between left- and right-sided RT was observed among patients with 0 to 2 cardiovascular risk factors, whereas left-sided RT was associated with significantly higher IHD risk among patients with 3 risk factors (adjusted sHR, 1.37; 95% CI, 1.10-1.71; Gray test P = .004). Conclusions and Relevance In this cohort study of 23 305 women with breast cancer, excess cardiac risk associated with left-sided RT was concentrated among patients with 3 cardiovascular risk factors. 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.
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Chung et al. (2026) conducted a cohort in Breast cancer (n=23,305). Left-sided breast radiotherapy vs. Right-sided breast radiotherapy was evaluated on Cumulative incidence of ischemic heart disease (IHD) (sHR 1.11, 95% CI 1.01-1.22, p=0.04). Left-sided breast radiotherapy was associated with a significant increase in ischemic heart disease risk compared to right-sided radiotherapy, with excess risk concentrated in patients with 3 cardiovascular risk factors.
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