OBJECTIVETo study the clinicopathologic characteristics of thymic epithelial tumors and to evaluate the diagnostic reproducibility and clinical relevance of the 2004 WHO histologic classification system.

METHODSThe morphology and immunophenotype of 52 cases of thymic epithelial tumor were reviewed. The tumors were classified according to the new WHO classification system and the clinical data were analyzed.

RESULTSOf the 52 cases studied, 45 were thymomas and 7 were thymic carcinomas. Amongst the 45 cases of thymoma, 6 (13.4%) were type A, 15 (33.3%) were type AB, 4 (8.9%) were type B1, 9 (20.0%) were type B2, 9 (20.0%) were type B3 and 2 (4.4%) were metaplastic thymoma. Amongst the 7 cases of thymic carcinoma, 6 were squamous cell carcinomas and 1 was neuroendocrine carcinoma. The commonest presentations were cough and chest pain. Some cases were incidentally discovered by routine physical examination. Thirteen cases (25.0%) of thymoma were associated with myasthenia gravis. CT scan showed that 49 cases (94.2%) were located in the anterior mediastinum. All cases of type A, AB and B1 thymoma and most cases of B2 thymoma appeared as well-defined homogeneous mass, whereas a few cases of type B2 thymoma and most cases of type B3 thymoma and thymic carcinoma were poorly demarcated and heterogeneous. According to Masaoka staging system, 20 cases (41.7%) belonged to stage I, 15 cases (31.3%) stage II, 11 cases (22.9%) stage III and 2 cases (4.1%) stage IV. The histologic subtypes of thymic epithelial tumors significantly correlated with the clinical stages (chi(2) = 32.5, P < 0.01).

CONCLUSIONSThe 2004 revision of WHO histologic classification system for thymic epithelial tumors shows a high degree of reproducibility. Correlation with the radiologic, clinical and prognostic parameters is helpful in determining the management strategy for individual patients.