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The information on this page was reviewed and approved by
Maurie Markman, MD, President, Medicine & Science at CTCA.

This page was updated on June 15, 2021.

Genetic testing

Cancer is caused by the uncontrolled growth of abnormal cells, a process triggered by mutations in the cells’ genes. As these cells multiply, they cluster together to form tumors or crowd out healthy cells in the bloodstream. Most cancers occur by chance or sporadically. Gene changes may result from a random mistake when cells divide. Genes may also change in response to lifestyle habits and/or environmental exposures or injuries.

People in some families have what is known as a hereditary cancer syndrome, a cancer risk that runs in the family. These syndromes are classified by a specific gene mutation or mutations that are passed down from one generation to the next. Certain syndromes may be linked to the risk of developing multiple cancers. For instance, patients with Lynch Syndrome, linked to the mutation of several genes, are at high risk of developing several reproductive or gastrointestinal cancers. Hereditary cancer syndromes are associated with 10 percent of all cancer diagnoses. However, not everyone who is born with a tendency for a gene mutation will develop cancer.

Hereditary risk assessment

During your initial evaluation period at Cancer Treatment Centers of America® (CTCA), you will fill out a questionnaire that includes questions about your personal and family history of cancer. This information will help determine whether you are a candidate for genetic testing.

The following are some indications of a hereditary cancer risk:

  • Family member with a known inherited gene mutation
  • Breast, colon or uterine cancer diagnosed under the age of 50
  • Ovarian cancer diagnosed at any age
  • Two or more close family members who have had the same type of cancer
  • The same type of cancer in several generations of the family

Genetic testing may be useful in helping you make informed decisions about how to manage future risks of cancer. For example, if it is determined that you are at greater risk than the “average” patient for breast cancer recurrence, we may recommend adding breast MRIs to your routine screenings. Also, if you are a woman who has breast cancer and you find out that you have an inherited risk, you may be at an increased risk for developing ovarian cancer. We will present you with options that may reduce that risk. If you already have cancer, testing may help determine whether it resulted from an inherited gene mutation or whether you are at an increased risk of developing a second cancer.

A genetic test requires a DNA sample that can be obtained from blood, saliva or a mouthwash sample. Before and after your test, you may choose to meet with a genetic counselor to discuss your questions and concerns. You will learn about the role of genes and hereditary in the development of cancer and which of your family members may be affected. The test results may also help your doctor develop a care plan individualized just for you.

Understanding genetic testing results

You may undergo a genetic test to determine whether your DNA includes one or more known inherited changes—called variants or mutations—associated with cancer. Experts think inherited variants cause 5 to 10 percent of all cancers, according to the National Cancer Institute (NCI).

The genetic test may be for a specific variant or a panel screening of your chromosomes for a wide group of changes.

Possible test results for each variant include:

  • Positive
  • Negative
  • Uncertain significance
  • Benign

What does a positive result mean?

If your test comes back positive, that means you have a variant known to be associated with cancer.

  • If you’ve already been diagnosed with cancer, the test may confirm that it was likely caused by this variant.
  • If you don’t have cancer, the test indicates you have a higher-than-normal chance of developing the types of cancer associated with the variant.

It may be wise to schedule regular screenings and make any lifestyle changes your doctor recommends to potentially lower the risk. For some cancers, medications may also be prescribed.

A positive result associated with a high risk may lead you to consider surgical removal of the tissue targeted by the cancer associated with that variant. Some women at high risk of ovarian cancer, for example, have opted to have their ovaries removed.

Most notably, many women have chosen to have their breasts removed after learning their cells carry one of these mutations:

  • BRCA1
  • BRCA2
  • PALB2
  • PTEN
  • TP53

Removal doesn’t eliminate all breast tissue, so a small chance remains that you may still get cancer. Surgery also affects the way you view your body, and it may change your sex life. Younger women have more risk reduction from removal, simply because they potentially have more years of life ahead of them. According to the NCI, bilateral prophylactic mastectomies may reduce cancer risk by 95 percent or more if you carry the BRCA1 or BRCA2 gene mutations, and by as much as 90 percent if you have a strong family history of breast cancer.

The NCI also estimates that removal of ovaries and fallopian tubes may cut the chances of developing ovarian cancer by about 90 percent and breast cancer by 50 percent, if you’re at high risk for these diseases.

Since genetic variants are most often inherited, at least one of your parents has it, and it may be passed on to your children.

It’s important to remember that a positive result doesn’t mean someone will develop cancer. Your oncologist or genetic counselor may help you better understand your situation.

What about a negative result?

A negative result means one of three things:

  • If testing for a specific variant (typically if a type of cancer runs in the family), a negative test result shows you don’t have that variant. In that case, you wouldn’t share the same cancer risk with other family members who have been tested and found to have the variant. This result is called a “true negative.” It doesn’t mean you have no risk of developing cancer; you just don’t have the increased risk of someone with that variant.
  • If your family has a notable history of cancer, but testing hasn’t found a common variant and you test negative for a possible variant, it’s termed an “uninformative negative.”
  • There’s also the chance of a false negative—the test failed to detect a variant you have in your genetic makeup. Genetic testing isn’t perfect, so inaccurate results are possible. Advances and refinements in testing continue to be made to give you the most accuracy possible.

One caveat—cancers that run in families aren’t always caused by a shared variant, but may be due to lifestyle choices (smoking, for example), diet or environmental exposures they have in common.

What is a variant of uncertain significance (VUS)?

When you’re found to possess a variant that’s of unknown or uncertain significance, it means health experts don’t yet know whether that genetic change is harmless or benign, or if it heightens your risk of getting cancer. Most of these variants eventually get classified as benign, but some are later discovered to be linked to cancer. For that reason, if you receive a finding of uncertain significance, you may wish to stay in touch with your doctor to see whether research eventually reveals whether the variant is innocuous or a threat.

Benign variants

Everyone has some changes in their DNA that scientists regard as harmless. Doctors call these common variants benign, or not suspected of causing disease. A test result of a benign variant shouldn’t cause you to worry—the variant isn’t on the list of those linked to cancer.

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