Background: Thymoma is an uncommon neoplasm derived from epithelial cells of the thymus. Few studies have addressed the genetic alterations that occur in the tumourigenesis of thymoma.
Methods: We examined aberrant DNA methylation of DAP-K, p-16, MGMT and HPP1 genes in 26 thymomas and 6 thymic carcinoma to clarify the association between aberrant DNA methylation and clinicopathological features.
Results: Fifteen (47%) of 32 thymic epithelial tumours showed aberrant methylation. Aberrant methylation was more frequent in thymic carcinoma (86%) than in thymoma (29%). Moreover, the frequency of tumours with methylation of multiple genes in thymic carcinoma was higher than in thymoma (60% vs 20%). In thymoma, the frequency of tumour methylation, including the type A tumour component (28%), was lower than that of tumours with type B tumour component (42%). MGMT methylation was detected in 23% of thymoma and in 83% of thymic carcinoma. The frequency of methylation of the MGMT gene in both tumours was high compared with the other 3 genes.
Conclusions: Aberrant DNA methylation was more frequent in thymic carcinoma than in thymoma, and the frequency of DNA methylation in thymic epithelial tumours is roughly parallel to their malignant behaviour.