DAPK1 and thymoma: The analysis of global methylation levels and of the promoter methylation status of the tumor suppressor genes (TSG) hMLH1, MGMT, p-16INK4a, RASSF1A, Fragile Histidine Triad Diadenosine Triphosphatase (FHIT), Anaphase-promoting complex subunit 1 (APC1A), Retinoic acid receptor β (RARB), Death-associated protein kinase (DAPK) and E-cadherin in 65 TEN samples revealed hypermethylation and decreased TSG expression in types B1 or higher thymomas.