IGF1 and cancer: Research analyzing exclusively the expression of the IGF1Ec peptide (MGF) in gastrointestinal tract NENs, i.e., gastric cancers (n = 8), pancreatic cancers (n = 17), small bowel cancers (n = 9), few cancers of unknown primary origin and appendiceal or gallbladder cancers (n = 8), report varying percentage of MGF expression (0–100% positive cases), localized solely to the tumor cell cytoplasm [32].