GAST and gastrointestinal disease: Apart from the normal physiology effects of gastrin activating the CCK2R signaling pathway, it is also found that CCK2R can be activated by gastrin in many gastrointestinal diseases including peptic ulcer disease, malignant tumors of the colon, pancreatic and gastric cancers, resulting in cell proliferation (Fourmy et al., 2011; Dimaline and Varro, 2014; Maddalo et al., 2014; Smith et al., 2016).