PTPRG and Merkel cell skin cancer: DNA methylation examination of MCPyV-positive and MCPyV-negative MCC specimens showed that 54% had hypermethylation of the RASSF1A promoter and 22% of the CDKN2A promoter, whereas the promoters of the tumor suppressor genes fragile histidine triad diadenosine triphosphate (FHIT), tumor promoter p73 (TP73), and protein tyrosine phosphatase receptor type G (PTPRG) had no or infrequent hypermethylation.