Genetic Counseling and Genetic Testing

Autor: OncoLink Team
Última Vez Revisión: 6 de abril de 2018

Genetic counseling and genetic testing go hand-in-hand. Patients are referred to a genetic counselor if a genetic syndrome is known or suspected to be present in a family.

Because genetic testing is a relatively new technology that relies on constantly evolving scientific discoveries, patients consult with genetic counselors and doctors to have a complete discussion about the meaning of test results. Some of the more common, earlier-discovered mutations have been well-studied, and their interpretation is supported by a large body of scientific evidence. On the other hand, other tests and mutations may be less well-understood by the scientific and medical community, and require an expert understanding of how to interpret these results. Genetic counselors and specialized doctors consult with patients specifically to discuss what the results (positive, negative or inconclusive) mean for the patient.

A genetic counselor thoroughly evaluates a patient's family history and risk factors, and helps the patient decide if genetic testing is appropriate. Part of the genetic counselor's initial consultation will be to discuss what genetic testing might show, the reliability of those test results, how inconclusive test results will be addressed, and the next steps if the test is positive for a genetic mutation. Once test results are available, the genetic counselor will explain them to the patient, answer questions, and help plan next steps.

When to consider genetic testing?

While cancer is not uncommon, there is a greater likelihood of a genetic syndrome if there is a pattern of cancers in a family (blood relatives). You might consider genetic testing if you have several family members with the same type of cancer, family members with different kinds of cancer diagnosed before age 60, or family members who were each diagnosed with multiple cancers. For instance, if a grandmother, a mother, and her two daughters were all diagnosed with breast cancer in their 30s, there is a good chance that a genetic syndrome is involved. On the other hand, if a grandmother and mother were diagnosed with breast cancer in their 70s, while the mother's daughters might be at increased risk of breast cancer later in life, it is unlikely that they share a genetic syndrome.

These genetic mutations are sometimes linked to people of a specific cultural or regional background. For example, people of Ashkenazi Jewish background are more likely to have BRCA1 and BRCA2 genetic mutations. If you are concerned about a cancer history in your family, talk to your care team about a referral to a genetic counselor.

Testing for Common Genetic Mutations

Genetic Testing for Breast and Ovarian Cancer

Between 5 and 10% of breast and ovarian cancers are caused by two gene mutations that run in families. These are called BRCA1 and BRCA2. These genes can be passed from a parent to a child. There are thousands of different gene mutations that can occur in the BRCA1 or BRCA2 genes. There is a misconception that these mutations are only a concern for women of Ashkenazi Jewish heritage. In actuality, only 3 of the mutations are associated with this ethnic background.

A mutation in BRCA1 or BRCA2 can be inherited from your mother or father. Females who inherit a mutation in the BRCA1 or BRCA2 gene have a higher risk of developing breast and/or ovarian cancer over their lifetime than someone in the general population. Males with BRCA 1 or BRCA2 are at a higher risk for developing prostate, colon and breast cancers than someone in the general population. Both males and females are also at a slightly higher risk than the general population for other cancers, including stomach or pancreatic cancer.

It is important to remember that not all individuals who have the BRCA1 and/or BRCA2 gene mutations will get cancer, they simply have a higher risk than people without the mutation. A genetic counselor can help determine the best preventive interventions, screening tests and screening schedule for a patient.

Genetic Testing for Colon Cancer

Most colon cancers are "sporadic", or have no hereditary link. However, some colon cancers (5% to 6%) are caused by a genetic mutation. Families with certain gene mutations have a higher lifetime risk of developing colon cancer.

There are three well documented forms of hereditary colorectal cancer:

  • Familial adenomatous polyposis (FAP) is a syndrome in which a person will develop many growths (called polyps) in the colon and rectum. This can occur in both males and females. These growths can occur in teenagers and young adults. A person will develop so many polyps that there is a high risk that one or several of them may turn cancerous. If not treated, most people with FAP will have developed colon or rectal cancer by the time they are 40 years of age. Individuals with FAP are also at risk for developing tumors in other parts of the body, including the thyroid, pancreas or liver.
  • Hereditary non-polyposis colorectal cancer (HNPCC) is also referred to as Lynch Syndrome. People with this mutation are at a higher risk than the average person for developing colon cancer. They are also at a higher risk for stomach, ovarian cancer and several other cancers.
  • APC I1307K: This mutation occurs on the same gene which causes APC. However, this mutation is found only in individuals of Ashkenazi Jewish descent.

Genetic Testing for Prostate Cancer

Between 5 and 10% of prostate cancer cases are thought to be due to inherited genetic factors. There is not one gene that causes prostate cancer. Research has shown that mutations on a number of genes are common in men who have prostate cancer. It is important to remember that having mutations on these genes does not mean that the person is guaranteed to develop prostate cancer.

Genetic testing for prostate cancer is most appropriate for a man with a strong family history of prostate cancer. A strong family history is usually described as one of the following:

  • Three or more first-degree relatives (father, brother, son).
  • Three successive generations of prostate cancer on either the mother’s or father’s side of the family.
  • At least two relatives affected at or before age 55 years.

The occurrence of prostate cancer is also linked to mutations in the BRCA1 and BRCA 2 genes that cause breast and ovarian cancer. If one or several family members have developed breast or ovarian cancer, the risk of developing prostate cancer in male family members may be higher.

What to do with the results?

If you are found to have a genetic mutation, it is important to educate yourself about the result and your risk. Your genetic counselor will help you understand what the results mean and how to act on them. Some results are called "inconclusive" or "unknown significance" - meaning they are not able to say you have a specific mutation, but you may have a mutation that has yet to be discovered. These results can be particularly challenging and talking with a counselor is vital to understanding the results and how to act on them.

Knowing your genetic risk for cancer can help you make informed decisions about screening, prevention and preventive treatments. There may be lifestyle changes you can make to reduce your risk of developing the cancer. Your providers may recommend a more aggressive plan of screening tests than the general public would have. You may be a candidate for surgical treatments or medications to reduce risk.

What to tell family members?

Once you receive the results of genetic testing, you may wonder how to discuss them with family members. This is a common concern that genetic counselors are very familiar with. Your genetic counselor will advise you about what to tell your family members, and will likely have advice on how to go about the conversation. What and how much to discuss will be dependent on your results. For instance, if your test results find a mutation that is related to a genetic syndrome, your genetic counselor may recommend that certain additional family members undergo testing.

Sharing information about risk can be lifesaving. When you tell a family member about your increased genetic risk, you are empowering them to learn more about their own health and make their own informed decisions about health care.

Resources for more information

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