Purpose: To assess the factors that predict local control and survival in patients with thymoma treated with adjuvant radiotherapy (RT) and suggest strategies for optimizing adjuvant RT.
Methods and materials: The study population comprised 47 patients with noninvasive thymoma and 128 patients with invasive thymoma. Treatment was surgery in 175 patients and radiotherapy in 169 patients; 25 patients also received adjuvant chemotherapy. The clinical factors (age, histologic features, stage, presence of myasthenia gravis) and therapeutic factors (extent of operation, irradiation dose, and field size) were retrospectively recorded and accessed using multivariate analysis.
Results: The overall survival rate at 5 and 10 years was 86.4% and 80.6%, respectively. Only 2 patients had a relapse in the noninvasive group. None died of thymoma during the study period. The patients with invasive disease had a 5- and 10-year disease-free survival rate of 64.4% and 55.6%, respectively, with 24 intrathoracic failures, 14 extrathoracic failures, and 8 combined failures. The univariate and multivariate analyses showed that Mosaoka stage and extent of resection were the important prognostic factors for patient with invasive thymoma. The 5-year survival rate and local control rate was 96% and 96% for Stage II, 77.8% and 56.4% for Stage III, 56.6% and 42.7% for Stage lVa, and 35.6% and 21.6% for Stage IVb (p < 0.0001 among different stage groups), respectively. The 5-year local control rate in patients with the tumor bed irradiated was 68.2%, comparable to the group treated with an extended RT field (66.6%). Age, histopathologic findings, radiation dose, and presence of myasthenia gravis were not statistically significant prognostic factors.
Conclusion: Disease stage and extent of resection affected the prognosis of invasive thymoma patients. Extending the radiation field prophylactically was not associated with greater local control and is of questionable value for patients with invasive thymoma.