Who should consider genetic counseling and testing and how is it conducted?
Genetic counseling followed by genetic testing should be considered for individuals as well as their family members when there are:
- Individuals in the family with early onset of colon cancer, before age 50
- Individuals in the family with numerous colon polyps
- Families in which multiple members have colon cancer
- Families with members with numerous colon polyps
- Families with members having colon cancers at young ages
- Families with members having certain non-colon cancers such as cancers of the uterus, thyroid, ureters, ovaries, small intestine, etc.
Genetic counseling both obtains the details of a patient's history, and helps them to understand what testing may be recommended and what the results could mean. Genentic testing is voluntary and the results cannot be used today to disqualify you from obtaining health insurance. Life insurance may be denied on the basis of such testing presently. Other concerns will be discussed as well.
Genetic testing without prior counseling is discouraged because of the extensive family education that is involved and the complicated nature of interpreting the test results.
Why is genetic counseling and testing important in hereditary colon cancer syndromes?
Patients who have hereditary colon cancer syndromes usually have no symptoms and are unaware that they have colon polyps or early colon cancers. They usually will develop colon cancers early in life (often before ages 40-50). Therefore, to prevent colon cancers in patients with hereditary colon cancer syndromes, colon screening must begin early. For example, patients with FAP should have annual flexible sigmoidoscopies starting at age 12, patients with AFAP should have annual colonoscopies starting at age 25, and patients with HNPCC should have colonoscopies beginning at age 25 (or 10 years younger than the earliest colon cancer diagnosed in the family, whichever is earlier). The current screening recommendations for the general population (fecal occult blood testing, flexible sigmoidoscopy, and colonoscopy beginning at ages 40-50) are inadequate for most patients with hereditary colon cancer syndromes.
Genetic counseling and testing are important to identify patients and family members with hereditary colon cancer syndromes so that screening with flexible sigmoidoscopies and colonoscopies can begin early and, if necessary, the colon can be removed surgically to prevent colon cancer. Moreover, depending on which hereditary colon cancer syndrome is present, early screening for other types of cancer such as ovarian, uterine, stomach, ureter, and thyroid may be appropriate.
How is genetic testing conducted?
Genetic testing should be done following genetic counseling, so that family members understand fully the advantages and limitations of genetic testing as well as how the tests should be interpreted.
Within the family, the first person to undergo genetic testing usually is the person who clearly has the disease (e.g., with numerous colon polyps with or without colon cancer). If genetic testing of this family member reveals a mutation responsible for a hereditary colon cancer syndrome, then other family members can be tested for the same mutation. Those family members who do not carry the mutation can be assured that they have not inherited the syndrome, whereas those who have the mutation should begin early screening for colon and other cancers. Depending on which syndrome is present and the age of the patient, removal of the colon may be recommended.
Unfortunately, genetic testing that shows no known cancer syndrome does not necessarily mean that there is no cancer syndrome. Our current knowledge about colon cancer syndromes is imperfect and our ability to recognize them is incomplete, and there may be unrecognized syndromes that cannot yet be detected. Even if no cancer syndrome is identified by genetic testing, first-degree relatives of someone with colon cancer are still considered at increased risk for developing colon cancer themselves and should undergo early screening as directed by their physicians.