Thymoma: a clinico-pathologic study based on newly developed morphologic criteria.

A retrospective study of 28 cases of thymoma classified according to Marino and Müller-Hermelink (cortical, medullary, mixed common, mixed with cortical predominance, mixed with medullary predominance thymoma) was undertaken to determine the existence of correlations between histology and clinical behavior. Cortical thymoma was observed in 11 cases (39.2%), mixed common thymoma in 9 (32.1%), mixed with cortical predominance in 5 (18%), and medullary thymoma in 3 (10.7%). In patients with cortical thymoma the tumor was always invasive (stages II and III according to Bergh), whereas medullary thymomas were noninvasive in 2 cases (stage I) and slightly invasive with a moderate infiltration of the capsule in the remaining case (stage II). Mixed common and mixed with cortical predominance thymomas displayed intermediate behavior. Twelve patients were affected by myasthenia gravis: 1 had medullary thymoma, 6 had mixed common thymoma, 3 had mixed thymoma with cortical predominance, and 2 had cortical thymoma. One patient with cortical thymoma had superior vena cava syndrome and 1 had erythroid hypoplasia; mixed common thymoma was associated with Cushing's syndrome in 1 patient. These data confirm previously reported observations (16) showing a higher degree of malignancy in patients with cortical thymoma.