Adjuvant radiotherapy for thymic epithelial tumor: treatment results and prognostic factors

To determine whether the use of adjuvant radiation in the treatment of invasive thymic tumors affects survival and to identify prognostic factors.

The files of 47 patients with thymic tumors treated by adjuvant radiation in our institute from 1984 to 2003 were reviewed for data on prognosis and survival. All patients underwent thoracotomy followed by either total macroscopic resection (n = 42) or biopsy (n = 5). The radiation dose ranged from 26 to 60 Gy.

Median duration of follow-up was 10.6 years. Overall 5-year survival was 73% (60%-88%): 77% for thymoma (n = 35/45) versus 33% for thymic carcinoma (n = 2/6) (P = 0.14). Better survival was associated with lower disease stage (II vs. III/IVA, P = 0.01), resection (P = 0.0004), myasthenia gravis at presentation (P = 0.04), and higher radiation dose (45 Gy, P = 0.02); sex, smoking, tumor size, pathology, and margin status had no effect. Locoregional relapse occurred in 11 patients and distant metastasis in 4. The 5-year disease-free survival was 67% (52%-86%), with a median time to recurrence of 8.3 years. The better overall survival and disease-free survival associated with higher doses of radiation were also true for stage II patients. On multivariate analyses after adjusting for age, higher disease stage and lower radiation dose were found to adversely affect overall survival and disease-free survival. Thymic carcinoma had an impact only on disease-free survival.

Postoperative radiation therapy to doses above 45 Gy may improve the disease-free and overall survival of patients with invasive thymoma, especially stage II. Thymic carcinoma has a worse prognosis.