THE CLINICOPATHOLOGICAL CORRELATION OF EPITHELIAL SUBTYPING IN THYMOMA - A STUDY OF 112 CONSECUTIVE CASES

The clinicopathological features of 112 thymomas collected from the su rgical pathological files of Taipei Veterans General Hospital from 196 1 to 1991 were investigated to determinate the clinical efficacy of ep ithelial subtyping. All thymomas were categorized based on the Muller- Hermelink system into three subtypes: cortical thymoma, mixed thymoma, and medullary thymoma. The former was further subclassified into orga noid thymoma, conventional cortical thymoma, and well differentiated t hymic carcinoma (WDTC) according to the systems of Pescarmona and Kirc hner. The association of each subtype with sex, age at diagnosis, clin ical stage, presence of myasthenia gravis, and length of survival was studied. As classified by the Muller-Hermelink system, the cortical th ymomas as a whole tended to occur in younger patients and were more fr equently associated with myasthenia gravis than the medullary thymomas . The cortical thymomas also showed a propensity to be invasive in nat ure, whereas the medullary thymomas generally behaved as benign tumors . Further subclassification of cortical thymomas into organoid thymoma , conventional thymoma, and WDTC did not provide more information abou t clinical behavior. By Kaplan-Meier's actuarial survival analyses non e of the epithelial subtypes displayed a statistically significant inf luence on prognosis. It is concluded that staging remains the most imp ortant factor affecting the patient's outcome. Because of the existenc e of many intermediate forms and the deficiency of clinical relevance, the subclassification of cortical thymomas should be interpreted as a morphological continuum rather than as distinct histological variants . HUM PATHOL 25:893-899. Copyright (C) 1994 by W.B. Saunders Company