Adjuvant radiotherapy and skin cancer risk in breast cancer survivors: a nationwide cohort study in Korea

Adjuvant radiotherapy (RT) is standard for breast cancer, but its impact on skin cancer risk, especially in Asian populations, remains unclear despite advanced techniques. This study aimed to assess skin cancer incidence following RT in a large South Korean cohort.

This retrospective cohort study, using South Korean Health Insurance Review and Assessment Service data (2009–2012), included 37,957 patients aged ≥20 with invasive breast cancer or ductal carcinoma in situ who underwent curative surgery. Prior malignancies or oncological treatment were excluded. Incidence of malignant melanoma and non-melanoma skin cancers were assessed. 1:1 propensity score matching was performed to balance confounders, resulting in 19,856 matched patients (9928 per group). Multivariable Cox proportional hazards models identified risk factors.

Post-matching, skin cancer incidence was comparable between RT and non-RT (NRT) groups (0.97% vs. 1.02%; p = 0.720). RT showed no significant association with overall skin cancer (p = 0.604), malignant melanoma (p = 0.094) or non-melanoma skin cancer (p = 0.196). Increased risk was associated with older age, mole presence (HR 5.254), pre-malignant skin lesions (HR 12.905), and lymphedema (HR 1.978).

Adjuvant RT did not increase skin cancer risk after breast cancer surgery. Dermatologic factors and lymphedema were principal predictors, emphasising vigilant follow-up in at-risk patients.