Does adjuvant radiation therapy improve disease-free survival in completely resected Masaoka stage II thymoma?

OBJECTIVE: To determine whether or not patients with completely resected Masaoka stage II thymoma benefit from postoperative radiotherapy (RT). METHODS: We retrospectively review the case records and compared the long-term outcomes of patients affected by Masaoka stage II thymoma treated by resection alone with same stage thymoma patients submitted to resection and RT. Surgical specimens were reviewed to confirm pathological stage, negative resection margins and histological subtype. RESULTS: Between 1988 and 2000, we performed 197 resections for thymoma; 58 patients resulted to be affected by completely resected tumours with microscopic transcapsular invasion (stage IIA, n=25) or macroscopic invasion into the surrounding fatty tissue with or without adhesion to the mediastinal pleura (stage IIB, n=33). Thirty-two patients underwent only complete surgical resection (14 stage IIA and 18 stage IIB); 26 patients underwent complete resection and subsequent mediastinal RT (11 stage IIA and 15 stage IIB). RT dosages were 45-54grays (Gy), in 25-30 fractions. Histological subtypes were similarly represented in both groups. Median follow-up was 91 months (range 9-170). Five intrathoracic recurrences occurred: three radiated patients (2 stage IIB - 1 AB and 1 B2 thymoma; 1 stage IIA B1 thymoma) and two not-radiated patients (1 stage IIA AB thymoma and 1 stage IIB B1 thymoma). Disease-free survival rate at 5- and 10-year were 94% and 87%, respectively. Log-rank test showed no difference in Kaplan-Meier survival curves (p=0.432) between radiated and not-radiated patients. CONCLUSIONS: These data support the concept that radical surgical resection alone should be considered a sufficient treatment for stage II thymoma.