PTPRO and cancer: The R3 subgroup of RPTPs includes density-enhanced phosphatase 1 (DEP-1), vascular endothelial protein tyrosine phosphatase (VE-PTP), stomach cancer-associated protein tyrosine phosphatase 1 (SAP-1), glomerular epithelial protein 1 (GLEPP1), and receptor-type protein tyrosine phosphatase Q (PTPRQ).