Postoperative radiation therapy for completely resected invasive thymoma: prognostic value of pleural invasion for intrathoracic control.

BACKGROUND

Optimal management of postoperative radiation therapy for completely resected invasive thymoma remains controversial. This study was conducted to assess the efficacy of postoperative mediastinal irradiation in patients with completely resected invasive thymoma.

METHODS

Between 1981 and 1996, 21 patients with completely resected invasive thymoma were referred for postoperative mediastinal irradiation. The distribution of Masaoka stages was stage II in 14 patients and stage III in seven patients. Nine patients had pleural invasion by the tumor. Thirteen patients were treated with a localized field and eight were treated with the whole mediastinal field with boost. The total dose to the primary tumor was 40-61 Gy (median: 52 Gy). The median follow-up time of the 16 living patients was 67 months (range: 29-202 months).

RESULTS

The 5- and 10-year actuarial overall survival rates in all patients were both 77%. Relapses were observed in five patients, in all of whom the sites of the first relapse involved pleural dissemination. There were no relapses within the irradiated field in any of the 21 cases. Five of nine (56%) patients with pleural invasion had relapse of pleural dissemination, while 0 of 12 (0%) patients without pleural invasion had relapse. In univariate analysis, pleural invasion had a statistically significant impact on intrathoracic control (P = 0.01).

CONCLUSIONS

The results indicated that pleural invasion might be predictive of pleural-based relapse for completely resected invasive thymoma. In patients with pleural invasion, mediastinal irradiation alone might be insufficient to avoid pleural-based relapse even after complete resection.