A number of factors may contribute to the formation of colon polyps and colon cancer. They include:
- Age. Most people with colon polyps are 50 or older.
- Inflammatory intestinal conditions. Long-standing inflammatory diseases of the colon, such as ulcerative colitis and Crohn's disease, can increase your risk.
- Family history. You're more likely to develop colon polyps or cancer if you have a parent, sibling or child with them. If many family members have them, your risk is even greater. In some cases this connection isn't hereditary or genetic. For example, cancers within the same family may result from shared exposure to a cancer-causing substance (carcinogen) in the environment or from similar diet or lifestyle factors.
- Tobacco and alcohol use. Smoking significantly increases your risk of colon polyps and colon cancer. Drinking alcohol, especially beer, in excess also makes it more likely that you'll develop colon polyps.
- A sedentary lifestyle. If you're inactive, you're more likely to develop colon cancer. This may be because when you're inactive, waste stays in your colon longer.
- Weight. Being overweight or obese has been linked to an increased risk of several types of cancer, including colon cancer.
- Race. If you are black or an Ashkenazi Jew of Eastern European descent, you are at higher risk of developing colon cancer.
Inherited gene mutations
Another risk factor for colon polyps is genetic mutations. A small percentage of colon cancers result from gene mutations. Some of these cancers are autosomal dominant, meaning you need to inherit only one defective gene from either one of your parents. If one parent has the mutated gene, you have a 50 percent chance of inheriting the mutation. Although inheriting a defective gene greatly increases your risk, not everyone with a mutated gene develops cancer.
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- Familial adenomatous polyposis (FAP). This is a rare, hereditary disorder that causes you to develop hundreds, even thousands, of polyps in the lining of your colon beginning during your teenage years. If these go untreated, your risk of developing colon cancer is nearly 100 percent, usually before age 40. The encouraging news about FAP is that in some cases, genetic testing can help determine whether you're at risk of the disease. People with FAP are also at risk of cancers of the small intestine, particularly in the duodenum.
- Gardner's syndrome. This less common syndrome is a variant of FAP. This condition causes polyps to develop throughout your colon and small intestine. You may also develop noncancerous tumors in other parts of your body, including your skin (sebaceous cysts and lipomas), bone (osteomas) and abdomen (desmoids).
- MYH-associated polyposis (MAP). This inherited condition is similar to FAP. People with MAP often develop multiple adenomatous polyps and colon cancer at a young age. Genetic testing can help determine whether you're at risk of MAP, which is caused by mutations in the MYH gene.
- Lynch syndrome. This condition, also called hereditary nonpolyposis colorectal cancer (HNPCC) is the most common form of inherited colon cancer. People with Lynch syndrome tend to develop relatively few colon polyps, but those polyps can quickly become malignant. Or, people with Lynch syndrome may have tumors in other organs, including the breast, stomach, small intestine, urinary tract and ovary, as well as in the colon.
- Peutz-Jeghers syndrome (PJS). This genetic condition usually begins with freckles developing all over the body, including the lips, gums and feet. Then benign polyps develop throughout the intestines. These polyps may become malignant, so people with this condition have an increased risk of colon cancer.
- Polyps of the colon and rectum. The Merck Manuals: The Merck Manual for Healthcare Professionals. http://www.merckmanuals.com/professional/sec02/ch021/ch021g.html#sec02-ch021-ch021e-1467. Accessed May 23, 2011.
- What I need to know about colon polyps. National Digestive Diseases Information Clearinghouse. http://digestive.niddk.nih.gov/ddiseases/pubs/colonpolyps_ez/. Accessed May 23, 2011.
- Colorectal cancer prevention and treatment. American Gastroenterological Association. http://www.gastro.org/patient-center/digestive-conditions/AGAPatientBrochure_ColorectalCancer.pdf. Accessed May 23, 2011.
- Ahnen DJ, et al. Approach to the patient with colonic polyps. http://www.uptodate.com/home/index.html. Accessed May 23, 2011.
- Detailed guide: Colorectal cancer. American Cancer Society. http://www.cancer.org/acs/groups/cid/documents/webcontent/003096-pdf.pdf. Accessed May 23, 2011.
- Torpy JM, et al. Colon polyps. Journal of the American Medical Association. 2008;300:1480.
- Itkowitz SH, et al. Colonic polyps and polyposis syndromes. In: Feldman M, et al. Sleisenger & Fordtran's Gastrointestinal and Liver Disease: Pathophysiology, Diagnosis, Management. 9th ed. Philadelphia, Pa.: Saunders Elsevier; 2010. http://www.mdconsult.com/books/about.do?eid=4-u1.0-B978-1-4160-6189-2..X0001-7--TOP&isbn=978-1-4160-6189-2&about=true&uniqId=229935664-2192. Accessed May 25, 2011.
- Ahnen DJ, et al. Colorectal cancer: Epidemiology, risk factors, and protective factors. http://www.uptodate.com/home/index.html. Accessed May 23, 2011.
- Tolliver KA, et al. Colonoscopic polypectomy. Gastroenterology Clinics of North America. 2008;37:229.