P2.04-002 The Efficacy of Postoperative Radiotherapy against Thymic Epithelial Tumors According to Masaoka Staging and WHO Classification: Topic: Thymic Malignancies Clinical and Translational

Abstract

Postoperative radiotherapy (PORT) against thymic epithelial tumors is mainly performed based on Masaoka staging. However there is no definite indication for PORT, and its efficacy is still controversial. Meanwhile, the relationship between the efficacy of PORT and WHO classification is also unclear. This study aimed to clarify the efficacy of PORT in association with both Masaoka staging and WHO classification. A 262 patients with thymic epithelial tumors surgically treated in our institute from April 1990 to December 2015 were reviewed. The clinicopathological data were retrospectively evaluated for prognosis and recurrence. There were 86 patients with stage I, 121 with stage II, 35 with stage III, 13 with stage IVa, and 7 with stage IVb thymic epithelial tumors according to Masaoka staging. As for histological type, 37 patients had type A, 50 had type AB, 59 had type B1, 43 had type B2, 44 had type B3, and 29 had type C (thymic carcinoma) according to WHO classification (2004). Eighty cases (30.5%) underwent PORT. Although PORT showed no association with OS (hazard ratio [HR], 0.565; 95% confidence interval [CI], 0.298 to 1.070; p=0.080), there was no recurrence in patients who received PORT. Subgroup analysis of Masaoka staging (stageI-II: HR, 2.445; 95% CI, 0.905-6.607; p=0.078, stage III-IV: HR, 0.434; 95% CI, 0.145 to 1.302, p=0.137,) or WHO classification (type A-B1: HR, 2.859; 95% CI, 1.050-7.719, p=0.030, type B2-C: HR, 1.460; 95% CI, 0.502 to 4.248; p=0.488) alone showed no association with prognosis either. However in thymoma patients who were classified in both stageIII-IV and type B2-C group, PORT was associated with better OS (HR, 0.189; 95% CI, 0.049 to 0.724; p=0.015). PORT is effective in patients with thyimic epithelial tumors who are classified in both stageIII-IV and type B2-C.