Colorectal (large bowel) cancer is a disease in which malignant (cancer) cells form in the inner lining of the colon or rectum. Together, the colon and rectum make up the large bowel or large intestine. The large intestine is the last segment of the digestive system (the esophagus, stomach, and small intestine are the first three sections). The large bowel's main job is to reabsorb water from the contents of the intestine so that solid waste can be expelled into the toilet. The first several feet of the large intestine is the colon and the last 6 inches is the rectum.
Most colon and rectal cancers originate from benign wart-like growths on the inner lining of the colon or rectum called polyps or flat lesions. The difference between polyps and flat lesions is primarily just their shape, with polyps growing more into the lumen than flat lesions. Not all polyps and flat lesions have the potential to transform into cancer. Those that do have the potential are called adenomas and sessile serrated polyps (also called sessile serrated adenomas). It takes more than 10 years in most cases for a precancerous polyp or flat lesion to develop into cancer. This is why some colon cancer prevention tests are effective even if done at 10-year intervals. This 10-year interval is too long, in some cases, such as in persons with ulcerative colitis or Crohn's colitis, in persons with a strong family history of colorectal cancer or adenomas, in persons who themselves have previously had colorectal cancer, and some persons who have had precancerous polyps or flat lesions
Colorectal cancer is the second most common cancer killer overall and third most common cause of cancer-related death in the United States in both males and females. Lung and prostate cancers are more common in men and lung and breast in women. In 2012, there will be 143,000 new cases and 52,000 deaths from colorectal cancer. About 6% of persons who reach the age of 50 in the United States will develop colorectal cancer without screening.
Symptoms of colorectal cancer vary depending on the location of the cancer within the colon or rectum, though there may be no symptoms at all. The prognosisis worse on average in symptomatic as compared to asymptomatic individuals (the latter refers to persons with cancer discovered by screening). The most common presenting symptom of colorectal cancer is rectal bleeding. Cancers arising from the left side of the colon generally cause bleeding, or in their late stages may cause constipation, abdominal pain, and obstructive symptoms. On the other hand, right-sided colon cancers may produce vague abdominal aching, but are unlikely to present with obstruction or altered bowel habit. Other symptoms such as weakness, weight loss, or anemia resulting from chronic blood loss may accompany cancer of the right side of the colon. You should promptly see your doctor when you experience any of these symptoms.
Precancerous polyps and flat lesions can grow for years and transform into cancer without producing any symptoms. By the time symptoms develop, it is often too late to cure the cancer, because it may have spread. Screening identifies cancers earlier and actually results in cancer prevention when it leads to removal of pre-cancerous growths
Screening means looking for cancer or polyps when patients have no symptoms. Finding colorectal cancer before symptoms develop dramatically improves the chance of survival. Identifying and removing polyps before they become cancerous actually prevents the development of colorectal cancer.
Several options are available for screening average-risk persons.
The strategy for reducing colorectal cancer deaths is simple.
Recent observations suggest regular use of non-steroidal anti-inflammatory drugs or aspirin, reduce the chances of colorectal cancer death by 30-50%. These drugs also have risks, particularly intestinal bleeding, and patients should consult their physician as to whether regular use of these agents is appropriate. Folate, calcium, and post-menopausal estrogens each have a modest protective benefit against colon cancer. A normal blood level of Vitamin D is associated with lower risk of colorectal cancer. A diet high in fiber and fruits and vegetables and low in fat diet, regular exercise, maintenance of normal body weight and cessation of smoking are also beneficial. None of the measures is as effective as or should replace colorectal cancer screening.
Suthat Liangpunsakul, MD and Douglas K. Rex, MD, FACG, Indiana University School of Medicine, Indianapolis, IN – Updated April 2007. Updated December 2012.
Suthat Liangpunsakul, MD and Douglas K. Rex, MD, FACG, Indiana University School of Medicine, Indianapolis, IN – Published October 2002.