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Inherited Colorectal Cancer

One of the risk factors for colorectal cancer is a family history of the disease. Colorectal cancer is called "hereditary" or "inherited" when several generations of a family have colorectal cancer. Several gene mutations, or abnormalities, that cause colorectal cancer, and allow it to be transmitted to family members, have been found. A gene is a block of DNA that holds the genetic code, or instructions, for producing proteins vital to our bodily functions.

The 2 most common inherited colorectal cancer syndromes are hereditary nonpolyposis colorectal 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.

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These 2 inherited cancer syndromes account for about 5% of all colorectal cancers.

Hereditary Nonpolyposis Colorectal Cancer (HNPCC), also known as Lynch syndrome

Nonpolyposis colorectal cancer, HNPCC, is the most common form of hereditary colon cancer, accounting for about 3% of all colorectal cancer diagnoses each year. People with HNPCC often have at least 3 family members and 2 generations with colorectal cancer, and cancer develops before age 50. Although not everyone who inherits the HNPCC gene will develop colorectal 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, renal pelvis, small intestine, and stomach cancer.

Health care providers can evaluate the pattern of colorectal 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:

  • At least 3 members (2 in small families) with colon or rectal cancer or 2 members with colorectal cancer and 1 with endometrial cancer, with other early-onset Lynch syndrome defined cancer
  • At least 2 successive generations with colon or rectal cancer
  • Two family members with the disease are first-degree relatives (i.e. parents, brothers, sisters or children) of another family member with colon and rectal cancer
  • At least 1 member affected at or before age 50
  • The familial adenomatous polyposis syndrome is excluded from the family member's diagnosis

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 characterized by the presence of more than hundreds or even thousands of benign polyps, or growths in the large intestine. It is thought to be present in about 1% of all people diagnosed with colorectal cancer each year. The polyps occur early in life, with 95% of people with FAP developing polyps by age 35, and are often detected in patients in their teens, with 50% developing polyps by age 15. If the colon is not surgically removed, there is a 100% chance that some of the polyps will develop into cancer, usually by age 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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