The search used the following terms: (A) “gastrointestinal” OR “digestive” OR “gastric” OR “pancreatic” OR “pancreas” OR “colorectal” OR “colon and rectum”; (B) “cancer” OR “carcinoma” OR “tumor” OR “tumor” OR “neoplasm”; (C) “Claudin18.2” OR “Claudin-18.2” OR “CLDN18.2” OR “Claudin18 isoform 2”; (D) “imaging” OR “image” OR “PET” OR “PET/CT” OR “SPECT” OR “fluorescence.” The search was restricted to English-language articles without temporal restrictions. Here, CLDN18 is linked to carcinoma.