Aberrant methylation of tumour-related genes in thymic epithelial tumours.

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.