Evaluation of a histogenetic classification for thymic epithelial tumours

We reviewed 87 thymic epithelial tumours from Chinese patients and typed them according to the Marino and Müller‐Hermelink classification as updated by Kirschner and Müller‐Hermelink in 1989. Related categories were grouped for statistical analyses; group 1, medullary thymoma and mixed thymoma; group 2, cortical predominant thymoma; group 3, cortical thymoma and well‐differentiated thymic carcinoma; group 4, other thymic carcinomas; and group 5, unclassified. Group 3 tumours were more frequently associated with the myasthenia gravis syndrome compared with group 1 tumours (P=0.001). They also presented at a more advanced stage. Groups 1 and 2 showed an excellent prognosis (100% survival at 10 years). The 10‐year survival for groups 3 and 4 patients was 40% and 30% respectively. Pure medullary thymoma made up a higher proportion of our cases (10.3%) than those of a similar Caucasian study (5.3%). The eight thymic carcinomas (group 4) included two thymic lymphoepitheliomas. We conclude that the histogenetic classification evaluated shows a clear correlation with prognosis and clinical features, even when tested on separate geographic groups, where pathogenetic factors may be different. A common approach to classification of thymic epithelial tumours would greatly facilitate future studies on these possible differences.