Lymphogenous and hematogenous metastasis of thymic epithelial tumors

A TNM classification has been established for various tumors. However, the TNM classification of thymic epithelial tumor has not been established yet.

We received replies to a questionnaire on thymic epithelial tumors from 115 institutes. We compiled a database of 1,320 patients with thymic epithelial tumor (1,093 thymomas, 186 thymic carcinomas, and 41 thymic carcinoids) who were treated between 1990 and 1994. We used a tentative TNM classification of thymoma presented by Yamakawa and associates in 1991. The regional lymph nodes of the thymus were classified into three groups: anterior mediastinal lymph nodes (N1), intrathoracic lymph nodes (N2), and extrathoracic lymph nodes (N3).

The rate of lymphogenous metastasis in thymoma, thymic carcinoma, and thymic carcinoid was 1.8%, 27%, and 28%, respectively. Most tumors with lymph node metastasis metastasized to N1 (thymoma, 90%; thymic carcinoma, 69%; thymic carcinoid, 91%). The 5-year survival rates of N0, N1, and N2 thymoma were 96%, 62%, and 20%, respectively. The 5-year survival rates of N0, N1(,) N2, and N3 thymic carcinoma were 56%, 42%, 29%, and 19%, respectively. The 5-year survival rates of M0 and M1 thymoma were 95% and 57%. The 5-year survival rates of M0 and M1 thymic carcinoma were 51% and 35%. Multivariate analysis demonstrated that survival of patients with thymoma was dependent on the clinical stage of Masaoka and complete resection. In thymic carcinoma, survival was dependent on lymph node metastasis and complete resection.

The N factor was one of the predictors of survival in thymoma and thymic carcinoma. However, M factor showed less influence on survival than T or N factors.