BACKGROUND: Therapy for young women with breast cancer (YWBC) in early stage includes surgery, radiotherapy, and endocrinotherapy. Radiation exposure, including from postoperative radiotherapy (PORT), is known to increase the risk of subsequent malignancies, particularly in younger individuals with longer life expectancy and greater tissue susceptibility. However, the long-term risk of second primary malignancy (SPM) associated with PORT specifically in YWBC remains poorly characterized. METHODS: In this retrospective cohort study using sing data from the Surveillance, Epidemiology, and End Results (SEER)-8 registries (1975-2018), we identified women aged 18-39 years diagnosed with localized or regional stage breast cancer. PORT-correlated risks were evaluated using multivariable logistic regression and Fine-Gray competing risk regression analysis. RESULTS: We identified 34,580 YWBC from the SEER database for our study, including 3,036 who developed SPMs. Logistic regression analyses indicated that PORT was associated with elevated odds of second primary solid malignancies (OR = 1.59, 95% CI 1.49-1.71), including breast cancer (OR = 1.99, 95% CI 1.82-2.17), lung cancer (OR = 1.73, 95% CI 1.39-2.18), and thyroid cancer (OR = 1.22, 95% CI 1.04-1.77). The cumulative incidence of SPMs, calculated using Fine-Gray competing risk regression, revealed similar findings: women who received PORT had significantly higher cumulative incidence of all SPMs (aHR = 1.52, p < 0.001) and SPSMs (aHR = 1.54, p < 0.001), consistent with the primary analysis results. Moreover, YWBC who were Black race, not married, estrogen receptor negative and progesterone receptor negative had a higher risk of developing SPMs. CONCLUSION: PORT for YWBC was associated with elevated risks of SPMs. The risk of PORT-related SPMs increased with a longer follow-up period, suggesting the need for long-term surveillance of these patients.
Wu et al. (Tue,) studied this question.