Cancer, colon: A malignant tumor arising from the inner wall of the large intestine. The third leading cause of cancer in males, fourth in females in the U.S. Risk factors for cancer of the colon and rectum (colorectal cancer) include heredity, colon polyps, and long standing ulcerative colitis. Most colorectal cancers develop from polyps. Removal of colon polyps can prevent colorectal cancer. Colon polyps and early cancer can have no symptoms. Therefore, regular screening is important. Diagnosis can be made by barium enema or by colonoscopy with biopsy confirmation of cancer tissue. Surgery is the most common treatment for colorectal cancer.
