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Colon Cancer and Genetic Testing

How does someone know if he or she may be a member of a family with FAP and may need genetic testing?

Patient Comments

An individual is likely to belong to a family with FAP if he or she has more than 100 adenomatous colon polyps or is a first-degree relative (parent, sibling, or child) of a person who has more than 100 adenomatous colon polyps. The number of polyps is less in some families, a condition referred to as attenuated FAP. Therefore, individuals who have between 20 and 100 adenomatous colon polyps or are first-degree relatives of individuals with 20 to100 adenomatous colon polyps also may belong to a family with FAP.

How is genetic testing for colon cancer risk done?

There has been much excitement during the past decade because of the identification of abnormal or defective genes (mutations) associated with colon cancer in families where colon cancer is common. When a defective gene can be identified, it is possible to examine other members of the family to see if they also carry the defective gene. Those individuals who carry the defective gene are at a very high risk (75%-100%) for developing colon cancer. The reason for the excitement is that if an individual is found to have the defective gene, his or her colon can be carefully monitored and then removed before the cancer occurs.

Only 5% of all colon cancers occur in families with a history of colon cancer and identifiable genetic defects. Therefore, genetic testing as it exists today is useful for only a minority of the about 130,000 people each year who are destined to develop colon cancer. Nevertheless, genetic testing is important because the risk is so extremely high among individuals who are found to have the genetic defect. In addition, more defective genes are likely to be found during the next few years, and this will make genetic testing valuable for an increasing number of individuals who will develop colon cancer.

At present, there are two types of familial colon cancer in which defective genes can be identified. One type of cancer is associated with a strong family history of colon polyps. The other type of colon cancer is not associated with a family history of colon polyps. The polyp-associated cancerous disease is called familial adenomatous polyposis (FAP). (Adenomatous polyps are a type of polyp that have the potential to become cancerous.) The nonpolyp-associated cancerous disease is called hereditary nonpolyposis colorectal cancer (HNPCC).

Medically Reviewed by a Doctor on 3/24/2017
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The eMedicineHealth doctors ask about Colon Cancer and Genetic Testing:

Colon Cancer Genetic Testing - Patient Experience

Were you tested for colon cancer risk? What steps did you take?

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Colon Cancer Symptoms

Cancer of the colon and rectum can exhibit itself in several ways. If you have any of these symptoms, seek immediate medical help. You may notice bleeding from your rectum or blood mixed with your stool.

  • People commonly attribute all rectal bleeding to hemorrhoids, thus preventing early diagnosis owing to lack of concern over "bleeding hemorrhoids." New onset of bright red blood in the stool always deserves an evaluation. Blood in the stool may be less evident, and is sometimes invisible, or causes a black or tarry stool.
  • Rectal bleeding may be hidden and chronic and may only show up as an iron deficiency anemia.
  • It may be associated with fatigue and pale skin due to the anemia.
  • It usually, but not always, can be detected through a fecal occult (hidden) blood test, in which samples of stool are submitted to a lab for detection of blood.
  • If the tumor gets large enough, it may completely or partially block your colon. You may notice the following symptoms of bowel obstruction.


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