Genetic Testing: Hereditary Colon Cancer

Medically reviewed by: Gary H. Hoffman, MD

Genetic testing is a preventative, potentially life-saving measure that helps in the early detection and treatment of asymptomatic, premalignant or malignant cancers.  Colon cancer is a common disease. Many colon cancers (and other, non-colon cancers) begin with an inherited genetic defect.  This defect can allow for the development of a cancer in an otherwise healthy colon, or trigger a cascade of events that stimulate the production of a malignancy within the lining of the colon or rectum.

The colon and rectum are part of the digestive system, and together are called the large intestine. The colon is a long muscular tube which moves fecal material, resorbs liquid and stores solid feces prior to its excretion.  The anal canal is the final storage tube and both stores feces and aids in its excretion.

When the normally smooth colon or rectal lining develops an overgrowth of tissue, polyps are formed.  Polyps are often premalignant. It is generally accepted that colorectal cancers begin as benign or harmless polyps.  Many of these polyps arise as a result of inherited genetic defects.

There are several forms of polyps or colon cancer that have known genetic defects.  These are:

  • Familial adenomatous polyposis (FAP)
  • Attenuated familial adenomatous polyposis (AFAP)
  • Hereditary nonpolyposis colorectal cancer (HNPCC), also known as Lynch syndrome.
  • MYH polyposis syndrome

Most patients with these genetic flaws have no symptoms or early warning signs.  Genetic testing and counseling are important forms of cancer prevention.  Early diagnosis and treatment can make a life saving difference.  It is crucial that surveillance and treatment are begun early in life for patients with hereditary risks for colon cancer. Certain conditions require initial screening as early as the onset of puberty.

Genetic counseling is recommended prior to genetic testing. Genetic counseling provides the patient and family the opportunity to fully understand the risks associated with genetic diseases.  Genetic counseling also provides the family with the ability to understand the advantages and limitations of genetic testing.

The first family member with a discovered hereditary colorectal cancer is called the proband. If genetic testing confirms a hereditary colon cancer syndrome in the proband, other family members may then be tested. If diagnosed with an inheritable form of the disease, patients may benefit from early, close surveillance or early treatment if the disease has already progressed.  Genetic testing is conducted either with testing of a sample of the tumor that has been removed from the proband, or, in possibly affected family members, through a cell sample obtained by gargling mouth wash and submitting the wash to a laboratory. Genetic testing is painless and can be conducted in your doctor’s office.

There are many reasons that a patient should consider genetic testing.  These include family traits such as:

  • Having 3 close relatives with microscopically confirmed colorectal cancer, 1 of whom is a first degree relative of the other 2.
  • Having at least 2 successive generations involved with colorectal cancer
  • Having at least 1 of the cancers diagnosed before age 50
  • Having one or more family members with certain related cancers such as endometrial cancer (cancer of the uterine lining), ovarian cancer, stomach or small bowel cancer, or other rare cancers.
  • Having a family member with a cancer that has been found to have features suggestive of an inheritable genetic cancer

If you are concerned about your risks for any form of colorectal cancer, you should make an appointment and speak with your physician.

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