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Adjuvant Radiotherapy for Stages II and III Resected Thymoma: A Single-institutional Experience

Introduction:The role of adjuvant radiation for Masaoka stages II and III thymoma remains controversial. The aim of this study was to evaluate the clinical benefit of radiation therapy for resected stages II and III thymoma patients. Methods:We retrospectively reviewed the medical records of 175 thymoma patients treated from July 1996 to January 2013 at University of Washington Medical Center; 88 patients with adequate follow-up and who met histologic criteria were included. We evaluated progression-free survival (PFS) and overall survival (OS), and compared these outcomes in patients treated by surgery (S) alone versus surgery plus radiotherapy (S+RT). Cox regression models and log-rank tests were used to compare PFS and OS for S versus S+RT, and they were further assessed by margin-positive versus margin-negative subgroups using Kaplan-Meier curves. Results:Among the 88 thymoma patients, 22 were stage II and 18 were stage III. For all stages II and III patients, adjuvant radiation was not identified as a significant predictor for PFS (P=0.95) or OS (P=0.63). A positive surgical margin predicted for a worse OS (hazard ratio=7.1; P=0.004). Further investigation revealed for resection margin-positive patients; S+RT had higher OS than S alone (P=0.006). Conclusions:For stages II and III thymoma, postoperative adjuvant radiation was not associated with statistically significant differences in PFS or OS in this study. Our results indicated a potential OS benefit of adjuvant RT in patients with positive resection margins, and therefore may be considered in this patient population.