STAT3 and central nervous system cancer: However, a related receptor-type protein tyrosine phosphatase, PTPRD, is thought play a role in regulation of STAT3 signaling and has been frequently implicated as a tumor suppressor in human cancers through inactivating somatic mutation, focal deletion or methylation in glioma, melanoma, neuroblastoma, colorectal, liver, head and neck, and lung cancers [119–122].