Causes of Colon Cancer

Close relatives (parents, brothers, sisters, or children) of a person with a history of colon cancer are somewhat more likely to develop this disease themselves -- especially if the relative had the cancer at a young age. If many close relatives have a history of colon cancer, the risk is even greater.

 

Changes in certain genes increase the risk of colon cancer. For example, hereditary nonpolyposis colon cancer (HNPCC) is the most common type of inherited (genetic) colon cancer. It accounts for about 2 percent of all cases of colon cancer. It is caused by changes in an HNPCC gene. About 3 out of 4 people with an altered HNPCC gene will develop colon cancer, and the average age at diagnosis is 44.

 

Another type of genetic colon cancer is familial adenomatous polyposis (FAP). This is a rare, inherited condition in which hundreds of polyps form in the colon and rectum. It is caused by a change in a specific gene called APC. Unless familial adenomatous polyposis is treated, it usually leads to colon cancer by age 40. FAP accounts for less than 1 percent of all colon cancer cases.

 

Family members of people who have HNPCC or FAP can have genetic testing done to check for specific genetic changes. For those who have changes in their genes, healthcare providers may suggest ways to try to reduce the risk of colon cancer or improve the detection of this disease. For adults with FAP, the doctor may recommend an operation to remove all or part of the colon and rectum.

 

A person who has already had colon cancer may develop colon cancer a second time. Also, women with a history of cancer of the ovary, uterus, or breast are at a somewhat higher risk of developing colon cancer.