Colon cancer is a disease that occurs when cancerous cells originate in the tissues of the colon. Some risk factors for the condition include having Crohn's disease, ulcerative colitis, or a history of colon polyps. In most cases, there are no early signs of the disease. When symptoms of the cancer do appear, they can include narrow stools, blood in the stool, and constipation or diarrhea. Rectal exams, fecal occult blood tests (FOBT), and colonoscopies are some of the tests doctors use to diagnose the cancer. Colon cancer may be treated with surgery, chemotherapy, radiation therapy, or a combination of treatments.