Rectal Cancer

Causes & Risk Factors

Having one or more of these rectal cancer risk factors listed below does not guarantee that a person will develop rectal cancer. It just increases the chances. People may want to talk with a doctor about these rectal cancer risk factors. The doctor may be able to suggest ways to reduce the chance of developing rectal cancer and can plan an appropriate schedule for checkups.

Rectal Cancer Causes: Who's at Risk?

The exact causes of rectal cancer are not known. However, studies show that the following risk factors of rectal cancer increase a person's chances of developing this disease:

Age. Colorectal cancer is more likely to occur as people get older. More than 90 percent of people with this disease are diagnosed after age 50. The average age at diagnosis is in the mid-60s. Diet. Studies suggest that diets high in fat (especially animal fat) and low in calcium, folate, and fiber may increase the risk of colorectal cancer. Also, some studies suggest that people who eat a diet very low in fruits and vegetables may have a higher risk of colorectal cancer. More research is needed to better understand how diet affects the risk of colorectal cancer.

Polyps. Polyps are benign growths on the inner wall of the colon and rectum. They are fairly common in people over age 50. Some types of polyps increase a person's risk of developing colorectal cancer.

A rare, inherited condition, called familial polyposis, causes hundreds of polyps to form in the colon and rectum. Unless this condition is treated, familial polyposis is almost certain to lead to rectal cancer.

Personal medical history. Research shows that women with a history of cancer of the ovary, uterus, or breast have a somewhat increased chance of developing colorectal cancer. Also, a person who has already had rectal cancer may develop this disease a second time.

Family medical history. First-degree relatives (parents, siblings, children) of a person who has had colorectal cancer are somewhat more likely to develop this type of cancer themselves, especially if the relative had the cancer at a young age. If many family members have had colorectal cancer, the chances increase even more.

Genetic alterations: Changes in certain genes increase the risk of colorectal cancer.

  • Hereditary nonpolyposis colon cancer (HNPCC) is the most common type of inherited (genetic) colorectal cancer. It accounts for about 2 percent of all colorectal cancer cases. It is caused by changes in an HNPCC gene. About 3 out of 4 people with an altered HNPCC gene develop colon cancer, and the average age at diagnosis of colon cancer is 44.

  • Familial adenomatous polyposis (FAP) 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 colorectal cancer by age 40. FAP accounts for less than 1 percent of all colorectal cancer cases.

    Family members of people who have HNPCC or FAP can have genetic testing to check for specific genetic changes. For those who have changes in their genes, health care providers may suggest ways to try to reduce the risk of colorectal cancer, or to 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.

Ulcerative colitis or Crohn's disease. A person who has had a condition that causes inflammation of the colon (such as ulcerative colitis or Crohn's disease) for many years is at increased risk of developing colorectal cancer.

Cigarette smoking. A person who smokes cigarettes may be at increased risk of developing polyps and colorectal cancer.

Reducing the Risk of Rectal Cancer

Research shows that rectal cancer develops gradually from benign polyps. Early detection and removal of polyps may help to prevent rectal cancer. Studies are looking at smoking cessation, use of dietary supplements, use of aspirin or similar medicines, decreased alcohol consumption, and increased physical activity to see if these approaches can help prevent rectal cancer. Some studies suggest that a diet low in fat and calories and high in fiber can help prevent rectal cancer.

Researchers have discovered that changes in certain genes (basic units of heredity) raise the risk of rectal cancer. Individuals in families with several cases of rectal cancer may find it helpful to talk with a genetic counselor. The genetic counselor can discuss the availability of a special blood test to check for a genetic change that may increase the chance of developing rectal cancer. Although having such a genetic change does not mean that a person is sure to develop colorectal cancer, those who have the change may want to talk with their doctor about what can be done to prevent the disease or detect it early.

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