PTPN22 and gastric cancer: As the Additional file 3 showed, levels of PTPN1, PTPN4 and PTPN12 were higher in esophageal cancer cell lines; PTPN2 and PTPN12 expressions were higher in stomach cancer cell lines; higher PTPN12 and decreased PTPN22 were identified in colorectal cancer cell lines.