PTPN22 and gastric cancer: Meanwhile, we detected the expression levels of circPTPN22 and its transcription gene PTPN22 using plasma from 20 GC patients and 20 healthy donors and found that only circPTPN22 had significant expression differences (P < 0.0001), while the transcription gene PTPN22 was not significantly different (P = 0.9567) (Fig. 2g).