Colon and Rectal Cancers - Causes

(Page 2)

People who inherit HNPCC and other defects are prone to other cancers, including uterine and ovarian cancers, as well as cancers of the small intestine and kidney system (very rare). HNPCC is highly associated with genes containing an abnormality called MSI (microsatellite instability), which is a sign of defective DNA repair. Testing tumors for MSI in people with newly diagnosed colon cancer who also have a family history of the disease may prove to be an effective method for identifying patients with HNPCC. Tests are being developed that can detect the actual HNPCC genetic abnormality (mutation) that was inherited from a father or mother. The two most commonly affected genes are MSH-2 and MLH-1.

---

---

Biochemical Factors Involved in Colon and Rectal Cancers

Cyclooxygenases and Prostaglandins. Cyclooxygenase 1 and 2 (COX-1 and COX-2) are enzymes involved in the production of prostaglandins, substances produced by the body that cause inflammation, widen and narrow blood vessels, control muscle contractions, and inhibit hormones that regulate fat metabolism. COX-2, but not COX-1, appears to play a role in the development and spread of colorectal tumors. COX-2 increases the levels of prostaglandin E2 (PGE2), which, in turn, stimulates factors that inhibit apoptosis, the natural process whereby all cells, including cancerous ones, self-destruct. It also activates interleukin-6 (IL-6), a factor in the immune system that is associated with cancer cell invasion.

C-Reactive Protein (CRP). CRP is another indicator of inflammation. In a 2004 study published in the Journal of the American Medical Association, elevated CRP levels predicted the development of colon -- but not rectal -- cancer.

Bile Acid Salts. Deoxycholic acid, which is found in the fat-digesting bile salts released by the gallbladder, appears to have carcinogenic properties. Its effects are now believed to play a role in some cases of colon cancer. Levels of the acid can rise as a result of high-fat diets or certain diseases.

Growth Factors. Chronically higher circulating levels of growth factors, including insulin-like growth factor (IGF), have been associated with colorectal cancer.

Inflammatory Bowel Disease

Inflammatory bowel diseases (IBDs) include Crohn's disease and ulcerative colitis. These chronic disorders cause persistent injuries in the intestinal tract that can, in some cases, produce cancerous changes.

Review Date: 03/06/2007
Reviewed By: A.D.A.M. Editorial Team: Greg Juhn, M.T.P.W., David R. Eltz, Kelli A. Stacy. Previously reviewed by Harvey Simon, M.D., Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital (9/1/2006).

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org).