Risk and prognosis of secondary esophagus cancer after radiotherapy for breast cancer.

Although radiation therapy (RT) improves locoregional recurrence and overall survival in breast cancer (BC), it is not yet clear whether RT affects the risk of patients with BC developing second esophageal cancer (SEC). We enrolled patients with BC as their first primary cancer from nine registries in the Surveillance, Epidemiology, and End Results (SEER) database between 1975 and 2018. Fine-Gray competing risk regressions were assessed to determine the cumulative incidence of SECs. The standardized incidence ratio (SIR) was used to compare the prevalence of SECs among BC survivors to that in the general population of the US. Kaplan-Meier survival analysis was applied to calculate the 10-year overall survival (OS) and cancer-specific survival (CSS) rates for SEC patients. Among the 523,502 BC patients considered herein, 255,135 were treated with surgery and RT, while 268,367 had surgery without radiotherapy. In a competing risk regression analysis, receiving RT was associated with a higher risk of developing an SEC in BC patients than that in the patients not receiving RT (P = .003). Compared to the general population of the US, the BC patients receiving RT showed a greater incidence of SEC (SIR, 1.52; 95% confidence interval [CI], 1.34-1.71, P < .05). The 10-year OS and CSS rates of SEC patients after RT were comparable to those of the SEC patients after no RT. Radiotherapy was related to an increased risk of developing SECs in patients with BC. Survival outcomes for patients who developed SEC after RT were similar to those after no RT.