The role of postoperative radiotherapy in stage II and III thymoma: a Korean multicenter database study

Background: Complete resection is a standard treatment for patients with Masaoka-Koga stages II and III thymoma, however the role of postoperative radiotherapy (PORT) is controversial. We analyzed data collected from 4 Korean hospitals to determine the effectiveness of PORT in stage II and III thymoma patients. Methods: Between January 2000 and December 2013, 1,663 patients underwent surgery for thymic tumors at the 4 hospitals. Among them, 668 patients (527 with stage II and 141 with stage III) were investigated, among whom, 443 received PORT (335 with stage II and 108 with stage III). Propensity score matching (PSM) was performed, and 404 patients (346 with stage II and 58 with stage III) were selected. Results: Perioperative characteristics were similar in the PORT and non-PORT groups after PSM. On survival analysis of stage II patients, the PORT and non-PORT groups showed no difference in either 5-year recurrence-free survival (RFS) (96.3% vs. 96.6%, P=0.622) or 5-year overall survival (OS) (94.6% vs. 93.8%, P=0.839). However, among stage III patients, the PORT group showed significantly better 5-year RFS (75.7% vs. 50.1%, P=0.040) and 5-year OS (86.5% vs. 54.7%, P=0.001). On multivariate Cox regression analysis, PORT was a significant positive prognostic factor in terms of both RFS (P=0.005) and OS (P=0.004) in patients with stage III thymomas, but not in those with stage II disease (P=0.987 and 0.968, respectively). Conclusions: PORT improved the RFS and OS in stage III thymoma patients, but showed no survival benefit in stage II patients.