There are five mammalian receptor PTPs in the R3 subgroup, CD148 (also known as DEP-1, PTPRJ), vascular endothelial protein tyrosine phosphatase (VE-PTP, PTPRB), glomerular epithelial protein 1 (GLEPP1, PTPRO), stomach cancer–associated protein tyrosine phosphatase-1 (SAP-1, PTPRH) and PTPRQ, which are characterized by an extracellular domain formed solely of multiple FN3 domains followed by a transmembrane domain and a single intracellular phosphatase domain [28]. The gene discussed is PTPRJ; the disease is cancer.