Thymoma is an uncommon neoplasm derived from thymus epithelial cells, and studies aimed at analyzing DNA methylation of tumour-related genes showed altered methylation patterns of many of them, including among others MGMT, hMLH1, p16/INK4, and RASSF1A, whose increased methylation significantly correlated with tumour severity [12,13]. The gene discussed is MLH1; the disease is neoplasm.