July 24, 2008

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Colon Cancer

Colon Cancer and Genetic Testing

Author: Jay W. Marks, MD
Editor: Michael Lill, MD

Find out about genetic testing for people with a family history of colon cancer.There has been much excitement during the past decade because of the identification of defective genes (mutations) associated with colon cancer in families where colon cancer is common. When a defective gene can be identified, it is possible to examine other members of the family to see if they also carry the defective gene. Those individuals who carry the defective gene are at a very high risk (75%-100%) for developing colon cancer. The reason for the excitement is that if an individual is found to have the defective gene, his or her colon can be removed before the cancer occurs.

Only 5% of all colon cancers occur in families with a history of colon cancer and identifiable genetic defects. Therefore, genetic testing as it exists today is useful for only a minority of the 130,000 people each year who are destined to develop colon cancer. Nevertheless, genetic testing is important because the risk is so extremely high among individuals who are found to have the genetic defect. In addition, more defective genes are likely to be found during the next few years, and this will make genetic testing valuable for an increasing number of individuals who will develop colon cancer.

At present, there are two types of familial colon cancer in which defective genes can be identified. One type of cancer is associated with a strong family history of colon polyps. The other type of colon cancer is not associated with a family history of colon polyps. The polyp-associated cancerous disease is called familial adenomatous polyposis (FAP). (Adenomatous polyps are a type of polyp that have the potential to become cancerous.) The nonpolyp-associated cancerous disease is called hereditary nonpolyposis colorectal cancer (HNPCC).

Find out about genetic testing for people with a family history of colon cancer »

Colon Cancer Overview

The human colon is a muscular, tube-shaped organ measuring about 4 feet long. It extends from the end of your small bowel to your anus, twisting and turning through your abdomen (belly). The colon has 3 main functions. 

  • To digest and absorb nutrients from food

  • To concentrate fecal material by absorbing fluid (and electrolytes) from it

  • To store and control evacuation of fecal material

The right side of your colon plays a major role in absorbing water and electrolytes, while the left side is responsible for storage and evacuation of stool.

Cancer is the transformation of normal cells. The transformed cells grow and multiply abnormally.

  • Left untreated, these cancers grow and eventually spread through the colon wall to involve the adjacent lymph nodes and organs. Ultimately, they spread to distant organs such as the liver, lungs, brain, and bones.

  • Cancers are dangerous because of their unbridled growth. They overwhelm healthy cells, tissues, and organs by taking their oxygen, nutrients, and space.

  • Most colon cancers are adenocarcinomas—tumors that develop from the glands lining the colon's inner wall.

  • These tumors are sometimes referred to as colorectal cancer, reflecting the fact that the rectum, the end portion of the colon, can also be affected.

In the United States, 1 in 17 people will develop colorectal cancer.

  • According to reports from the National Cancer Institute, colorectal cancer is the third most common cancer in US men.

  • Colorectal cancer is the second most common cancer in US women of Hispanic, American Indian/Alaska Native, or Asian/Pacific Islander ancestry, and the third most common cancer in white and African American women.

  • The overall incidence of colorectal cancer increased until 1985 and then began decreasing at an average rate of 1.6% per year.

  • Deaths from colorectal cancer rank third after lung and prostate cancer for men and third after lung and breast cancer for women.



Next: Colon Cancer Causes »


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