Causes of Rectal Cancer
Changes in certain genes increase the risk of rectal cancer. For example, hereditary nonpolyposis colorectal cancer (HNPCC) is the most common type of inherited (genetic) colorectal cancer. It accounts for about 2 percent of all cases of colorectal cancer. It is caused by changes in an HNPCC gene.
Another type of genetic rectal 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 rectal cancer by age 40. FAP accounts for less than 1 percent of all rectal 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 rectal 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.