Focusing on gastric, pancreatic, and colon cancer, we review information regarding the distribution of neural and non-neural sources of ACh and other agents reported to modulate muscarinic receptor function by direct or allosteric interactions, the distribution and expression of the five muscarinic receptor subtypes (M1R–M5R, encoded by CHRM1–CHRM5), and their differential roles in modulating cancer cell behavior. This evidence concerns the gene CHRM1 and cancer.