Rectal cancer: A malignant tumor arising from the inner wall of the final part of the large intestine -- the rectum. Although colon cancer and rectal cancer share many features, there are important differences between these two diseases including, especially, the tendency for rectal cancer -- but not colon cancer -- to recur locally. Local recurrence of rectal cancer is common (15-45%) after standard surgery and is often catastrophic. It is difficult to cure, and the associated symptoms are debilitating. Accordingly, preventing local recurrence is one of the main treatment goals with rectal cancer.
The prognosis (outlook) with rectal cancer is clearly related to the degree of penetration of the tumor through the bowel wall and the presence or absence of lymph node involvement. These two characteristics form the basis for all staging systems developed for this disease. Locally advanced or locally recurrent rectal cancer causes disabling symptoms and is difficult to treat.
The standard surgical procedure is called abdominal perineal resection with total mesorectal excision and a permanent end colostomy. Preoperative chemoradiotherapy has been found to reduce the risk of local recurrence and to cause fewer long-term toxic effects than if the chemoradiotherapy is given postoperatively. At five years, the overall survival among patients with locally advanced rectal cancer, irrespective of whether they have had preoperative or postoperative chemoradiotherapy, is about 75%.
Risk factors for rectal cancer include heredity (family history), colorectal polyps, and long-standing ulcerative colitis. Most cancers of the rectum, like those in colon, develop from polyps. Polyp removal can thus prevent rectal cancer. Polyps and early cancer can have no symptoms so regular screening is important. Diagnosis of rectal cancer can be made by proctoscopy or by colonoscopy with biopsy confirmation of the cancer.