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Bowel cancer health centre

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Inherited bowel cancer

One of the risk factors for bowel cancer, or colorectal cancer, is a family history of the disease. We refer to bowel cancer as being "hereditary" or "inherited" when several generations of a family have bowel cancer. Several gene mutations, or abnormalities, that cause bowel cancer, and allow it to develop in family members, have been found. A gene is a block of DNA that holds the genetic code, or instructions, for producing a protein vital for our bodily functions.

The two most common inherited bowel cancer syndromes are hereditary nonpolyposis bowel cancer (HNPCC) and familial adenomatous polyposis (FAP). They can affect either sex, and the children of people who carry these genes have a 50% chance of inheriting the disease-causing gene.

These two inherited cancer syndromes account for about five percent of all bowel cancers.

Hereditary nonpolyposis bowel cancer (HNPCC)

Hereditary nonpolyposis bowel cancer, HNPCC, is the most common form of hereditary colon cancer, accounting for around 2% to 5% of all bowel cancer diagnoses each year. People with HNPCC often have at least three family members and two generations with bowel cancer, and cancer develops before the age of 50. Although not everyone who inherits the HNPCC gene will develop bowel cancer, the risk is very high - about 80%. People with HNPCC also have a higher risk of developing other cancers, such as kidney, ovarian, uterine, bladder, small intestine, and stomach cancer.

Doctors can evaluate the pattern of bowel cancer in relatives in order to determine if the family has HNPCC. Families considered to be "HNPCC families" must display certain criteria indicating a pattern of colon cancer throughout generations. These are referred to as the Amsterdam Criteria, and include:

  • Three or more relatives with an associated cancer (colorectal cancer or cancer of the endometrium, small intestine, ureter or renal pelvis);

  • Two or more successive generations affected;
  • One or more relatives diagnosed before the age of 50;
  • One should be a first-degree relative of the other two;
  • Familial adenomatous polyposis (FAP) should be excluded in cases of colorectal carcinoma;
  • Tumours should be verified by pathologic examination.

If you feel this applies to you, consult your doctor. Colonoscopies are recommended in family members who are 10 years younger than the youngest family member who was diagnosed with cancer.

Familial adenomatous polyposis (FAP) syndrome

Familial adenomatous polyposis (FAP) is a rare condition characterised by the presence of more than 100 benign polyps, or growths in the large intestine. It is thought to be present in about 1% of all people diagnosed with bowel cancer each year. The polyps occur early in life and are often detected in patients in their teens. If the colon is not surgically removed, there is a 100 percent chance that some of the polyps will develop into cancer, usually by the age of 40.

While most cases of FAP are inherited, nearly a third of the cases are the result of a spontaneous (newly-occurring) gene mutation, or abnormality. For those who develop a new gene mutation, it is possible to pass the FAP gene onto their children.

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