REG4 and gastric cancer: According to the signature expression markers of stomach cells (Fig. 4), we identified CD4 + T cells, CD8 + T cells, mucous cells (TFF1 + and MUC5AC +), intestinal mucous cells [REG4 + and SPINK4 +], Chief cells (PGC +), and the potential gastric cancer cells (ALDH1A2 + and EPCAM +) completely derived from gastric cancer tissues.