Genetic Risk Factors for Colorectal Cancer

Martin G. Prosky, MD, FACP Gastroenterology Medical Director, Inova HealthSource Northern Virginia Gastrointestinal Associates, Ltd.

Q:  How common is colon cancer?
Cancer of the colon and the rectum represents a major cause of illness and death in the United States. Six percent of the American population will eventually develop invasive colon cancer. Colorectal cancer is the second leading cause of cancer death, second only to lung cancer. Over 6,000,000 Americans who are alive today will die of colon cancer.

Q:  Who gets colon cancer?
Colon cancer affects men and women. The risk of colon cancer increases with age.

Q:  Are there genetic factors that put some people at greater risk of developing colon cancer?
Current concepts concerning the causes of colon cancer have centered on the role of environment and the role of genetics. With advances in molecular biology and genetics, multiple abnormalities have been found in genes that can increase the risk of colorectal cancer. It is clear that there is a strong genetic predisposition in a substantial number of colorectal cancers. Genetic susceptibility to colorectal cancer in the general population is suggested by the two-to-three fold increase in colorectal cancer in first-degree relatives (parents and siblings) of patients with polyps and colorectal cancer. The risk is even stronger when cancer occurs in family members younger than 50.

There are many well-known familial colon cancer syndromes. These fall under the names of Familial Adenomatous Polyposis, Gardner's Syndrome, and Hereditary Nonpolyposis Colorectal Cancer. The latter, Hereditary Nonpolyposis Colorectal Cancer or HNPCC, is characterized by families that have at least three relatives with colon cancer, one of whom is a "first-degree relative" (parent or sibling) of the other two. In addition, the colorectal cancer occurs in at least two generations and in at least one case before the age of 50. In this genetic colon cancer syndrome, colon cancer occurs at an alarming high rate of 50 percentage.

Q:  Why is it so important to share my family's medical history with my doctor?
Knowing one's family history is extremely important since there are now effective ways to screen for colon cancer. We can screen those people at increased risk because of family history early to prevent the disease, or detect it at an early, curable stage. The hallmark of preventive screening consists of finding a polyp. A polyp represents a precancerous growth. It is well known that all cancers of the colon (except in inflammatory bowel disease) begin as a precancerous growth known as a polyp. Over the course of several years, colon polyps can evolve with increased growth and result in development of colon cancer.

Resources:
Hereditary Colon Cancer
Hereditary Colorectal Cancer
HCCA - The Prevention Webvocate