Long‐term outcomes and patterns of failure in patients with thymic malignancies treated with surgery and radiation therapy

Background The role of peri‐operative radiation therapy in thymic epithelial tumors remains controversial, and randomized data are lacking. The authors evaluated recurrence patterns, pathologic predictors of recurrence, and long‐term survival among patients who underwent surgery and received peri‐operative radiation at a high‐volume tertiary center. Methods The authors conducted a retrospective cohort study of patients who had thymic malignancies treated surgically between 2004 and 2021. Clinical, pathologic, and treatment data were collected. Outcomes were assessed using Kaplan–Meier and Cox regression methods, and propensity score overlap weighting was applied to adjust for baseline differences between the radiation and no‐radiation groups. Results In total, 360 patients were included, of whom 175 (48.6%) received peri‐operative radiation. Among irradiated patients, 62 (35.4%) developed recurrence, most commonly in the pleura (76%); in‐field recurrences were rare (5%). Tumor invasiveness was the strongest predictor of recurrence, particularly vascular invasion (odds ratio, 6.0; 95% confidence interval, 2.3–15.7). Histologic subtype was not associated with recurrence. Survival did not differ between groups on unadjusted comparison (hazard ratio, 1.02; 95% confidence interval, 0.63–1.67; p = .93). After overlap weighting, radiation was associated with overall survival (hazard ratio, 0.49; 95% CI, 0.26–0.90; p = .02). Conclusions In patients with surgically treated thymic malignancies, tumor invasiveness, especially vascular invasion, was the strongest predictor of recurrence and should guide risk stratification. Failure was predominantly pleural, with rare in‐field recurrence, indicating good local control but a need for better strategies against pleural relapse. Survival benefit from peri‐operative radiation remains uncertain and should be tested prospectively.