Postoperative radiotherapy after extirpative surgery may not improve survival in patients with Masaoka-Koga stage IIB thymoma: a propensity-matched study based on the SEER database

Background: The exact role of postoperative radiotherapy (PORT) in patients with Masaoka-Koga stage IIB thymoma following extirpative surgery (defined as radical surgery or total thymectomy) is still under debate. This study was designed to evaluate the effect of PORT on survival in patients with stage IIB thymoma following extirpative surgery in a population-based registry. Methods: Patients with Masaoka-Koga stage IIB thymoma who underwent extirpative surgery between 2000 and 2019 were identified from the Surveillance, Epidemiology, and End Results (SEER) database. One-to-one propensity score matching (PSM) with Kaplan-Meier and Cox regression analyses were used to assess overall survival (OS) and cancer-specific survival (CSS). To identify potential patients who may benefit from PORT, exploratory subgroup analyses on survival and further analyses stratified by Asian patients were performed. Results: A total of 273 eligible patients were included, 164 (60.1%) in the PORT group and 109 (39.9%) in the non-PORT group. After 1:1 PSM, OS and CSS were not significantly different between the two groups. The 10-year OS and CSS rates were 83.5% in the PORT group vs. 80.1% in the non-PORT group (P=0.95) and 97.8% vs. 97.7% (P=0.31), respectively. The multivariate analyses further demonstrated no significant association between PORT and either OS [hazard ratio (HR) =1.219, P=0.53] or CSS (HR =2.304, P=0.32). Exploratory subgroup analyses revealed that PORT did not significantly improve survival in any subgroup of patients with stage IIB thymoma, and further analyses based on the Asian patients yielded the same negative results. Conclusions: According to the SEER database, adding PORT to extirpative surgery may not improve survival in patients with Masaoka-Koga stage IIB thymomas.