Genetic Testing: What You Need to Know

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What is genetic testing?

Genetic testing is the process of using medical tests to look for changes (mutations) in a person’s genes or chromosomes. Hundreds of different genetic tests are used today, and more are being developed.

Genetic testing for diseases that can be inherited

Genetic testing can be used in different situations. The type of testing most often used to check for cancer risk is called predictive gene testing. It’s used to look for gene mutations that might put a person at risk of getting a disease. It’s usually done in families with a history that suggests there’s a disease that may be inherited. An example is testing for changes in the BRCA1 and BRCA2 genes (known breast cancer genes) in a woman whose mother and sister had breast cancer.

Genetic testing is also used for other reasons:

  • Carrier testing can be used to help couples learn if they carry a gene mutation for a disorder they might pass on to a child, such as cystic fibrosis, sickle-cell anemia, or Tay-Sachs disease.
  • Prenatal screening can be used to diagnose some conditions in babies before they are even born, such as Down syndrome.
  • Newborn screening is the most widespread form of genetic testing. Newborns are screened for a number of inherited conditions such as phenylketonuria (PKU), cystic fibrosis, sickle cell disease, and others. The tests required vary from state to state.

All of these forms of genetic testing, including predictive gene testing, look for gene changes that are passed from one generation to the next and are found in every cell in the body. Except for the newborn screening tests, they are used mainly for people with certain types of disease that seem to run in their families. They are not needed by most people.

Genetic testing for cancer risk

Cancer-related genetic tests are most commonly done as predictive genetic tests. They may be used:

  • To see if a person has a certain gene mutation known to increase the risk for a certain cancer (or cancers)
  • To confirm a suspected gene mutation in a person or family

Testing cancer cells for genetic changes

Sometimes after a person has been diagnosed with cancer, the doctor will order tests to look for gene changes in a sample of the cancer cells. These tests can give information on a person’s outlook (prognosis) and can sometimes help tell whether certain types of treatment might be useful.

These types of tests look for gene changes only in the cancer cells that are taken from the patient. These tests are not the same as the tests used to find out about inherited cancer risk.

This document does not cover gene testing done on cancer cells. For more about this kind of testing and its use in cancer treatment, see our information on specific types of cancer.

The rest of this document focuses on predictive genetic testing for inherited mutations as they relate to cancer.

Last Medical Review: 10/18/2013
Last Revised: 03/11/2015