The methylation levels of the DNA repair and tumor suppressor genes MLH1, MGMT, CDKN2A, and RASSF1A have frequently been investigated in thymic epithelial tumors (TETs), including thymomas (Hirabayashi et al., 1997; Suzuki et al., 2005; Chen et al., 2009; Hirose et al., 2009; Mokhtar et al., 2014; Kajiura et al., 2017). The gene discussed is RASSF1; the disease is thymoma.