Colon diseases are conditions that affect the colon, rectum, or anal canal. These include cancer, polyps, inflammatory bowel disease, diverticulitis, and irritable bowel syndrome. Colon diseases Colorectal cancer: Usually starts as polyps, which are noncancerous growths in the colon. Colonic polyps: Extra tissue in the colon that can become cancerous. Ulcerative colitis: Ulcers in the colon and rectum. Diverticulitis: Inflammation or infection of pouches in the colon. Irritable bowel syndrome: A