Postoperative radiotherapy is effective for thymic carcinoma but not for thymoma in stage II and III thymic epithelial tumors: The Japanese Association for Research on the Thymus Database Study

BACKGROUND The efficacy of postoperative radiotherapy (PORT) for thymic epithelial tumors is still controversial. Using the Japanese Association for Research on the Thymus (JART) database, this study was aimed at clarifying the efficacy of PORT for Masaoka stage II and III thymic carcinoma and thymoma. METHODS The JART database registered the records of 2835 patients collected from 32 Japanese institutions from 1991 to 2010. Thymic carcinoma and thymoma at stage II or III were extracted. The efficacy of PORT with respect to relapse-free survival (RFS) and overall survival (OS) was evaluated with the Kaplan-Meier method and Cox regression analysis. RESULTS There were 1265 patients in all: 155 thymic carcinoma cases (12.3%) and 1110 thymoma cases (87.7%). Eight hundred ninety-five (70.8%) were at stage II, and 370 (29.2%) were at stage III. Four hundred three cases (31.9%) underwent PORT. PORT for stage II and III thymic carcinoma was associated with increasing RFS (hazard ratio, 0.48; 95% confidence interval, 0.30-0.78; P = .003) but was not associated with OS (hazard ratio, 0.94; 95% confidence interval, 0.51-1.75; P = .536). PORT for stage II and III thymoma was not associated with RFS or OS (P = .350). A subgroup analysis of stage III thymoma showed no factor associated with the efficacy of PORT. CONCLUSIONS In this study, PORT did not increase RFS or OS for stage II or III thymoma but increased RFS for stage II and III thymic carcinoma. Cancer 2015;121:1008-1016.