[…] in stool; Diagnose the reason for chronic diarrhea; Screen the colon if abnormal results come back from a stool or barium enema test; Diagnose inflammatory bowel disease (IBD); Diagnose the reason for unexplained abdominal pain. [barnesjewish.org]

[…] in stool - colonoscopy Chernecky CC, Berger BJ. [nlm.nih.gov]

They look for blood in stool, but cancerous polyps do not always cause bleeding, so they are limited in their ability to detect all cancers. These types of tests may be less invasive, but they also are less accurate than colonoscopy. [healthplans.providence.org]