Left-Sided Radiotherapy Linked to IHD in Higher-Risk Women

Left-sided postoperative breast radiotherapy was associated with a modestly higher ischemic heart disease (IHD) risk than right-sided treatment in a nationwide Korean cohort, but the statistically significant difference in risk-stratified analyses was confined to women with 3 baseline cardiovascular risk factors, according to a study published in JAMA Network Open.

The retrospective cohort study used Korean National Health Insurance Service data and included 23,305 women who received postoperative radiotherapy for breast cancer from 2002 through 2018 and had no prior IHD. Median follow-up was 4.3 years. Tumor laterality served as a surrogate for cardiac radiotherapy exposure. Investigators calculated cardiovascular risk burden from 6 factors: age 55 years or older, obesity, smoking, hypertension, diabetes, and dyslipidemia.

Across the full cohort, 8-year cumulative IHD incidence was 11.1% after left-sided radiotherapy and 9.9% after right-sided treatment (P=.03). In multivariable competing-risk analysis, left-sided treatment was associated with an 11% higher IHD risk (subdistribution hazard ratio, 1.11; 95% CI, 1.01-1.22; P=.04).

Among women with 3 risk factors, 8-year IHD incidence was 20.3% with left-sided treatment and 15.2% with right-sided treatment, an absolute difference of 5.1 percentage points. The adjusted subdistribution hazard ratio was 1.37 (95% CI, 1.10-1.71), with Gray test P=.004. Differences were not statistically significant among women with 0 to 2 risk factors or those with 4 or 5 factors; confidence intervals were wide in the smaller 4- and 5-factor groups.

Limitations included reliance on claims data, absence of individual heart-dose measurements, use of laterality as a surrogate for cardiac exposure, and inability to capture increased use of cardiac dose-sparing techniques during the study period. The investigators characterized their cardiovascular risk score as hypothesis-generating and said it requires external validation before clinical use.

Source: Chung SY, Noh OK. Laterality of breast radiotherapy and ischemic heart disease by cardiovascular risk burden. JAMA Netw Open. 2026;9(9):e2631356. doi:10.1001/jamanetworkopen.2026.31356