Thymoma-a clinico-pathological long-term study with emphasis on histology and adjuvant radiotherapy dose

To evaluate prognostic factors of thymic epithelial tumors (TETs) with particular reference to histology and the dose-response relationship of adjuvant radiotherapy.

Retrospective study with central pathological review on patients resected for TET between 1966 and 2004 at a single institution. Prognostic factors were identified using Cox regression analysis.

From 93 patients with TET, 33.3% relapsed and 47.3% died. Cause of death was known in 64% and attributed to TET in 25%. Myasthenia gravis was associated with superior disease-free survival (DFS) and overall survival (OS). Tumors smaller than 8.5 cm had a significantly better prognosis. With a median follow-up of 9.8 years actuarial OS at 5, 10, and 20 years were 96%, 92%, and 47% in stage I; 85%, 61%, and 53% in stage II; 72%, 39%, and 15% in stage III and IV. Advanced stage and incomplete resection had a negative impact on DFS and OS. According to histology (WHO type A, AB, B1; favorable; versus WHO type B2, B3; intermediate; versus thymic carcinoma, unfavorable) three prognostic groups were discernible. On multivariate analysis, tumor size, and stage emerged as prognostic factors, but neither histology nor myasthenia. Postoperative radiotherapy was administered in 27 patients (median dose 50.8 Gy). Doses in excess of 50 Gy were associated with significantly improved DFS and OS.

Tumor stage, histology, complete resection, and tumor size had a significant impact on survival. Myasthenia may facilitate early detection and is correlated with superior survival. When postoperative radiotherapy is administered, doses above 50 Gy may improve outcome.