Biomarker tests and cancer treatment

Many types of "biomarkers"⁠—abnormal proteins, genetic material (genes, chromosomes, DNA and RNA), cellular material and other products⁠—are found in cancer cells, surrounding tissues or the blood. Doctors use biomarker tests to help detect cancer, select the best treatment, predict how fast the cancer will grow and spread and monitor response to therapy. 

Biomarker tests can be confusing. There are many different types of biomarkers and different tests to measure them. Experts do not always use the same names for the same biomarker tests, which adds to the confusion. And some terms apply to more than one type of test. Requesting a copy of your medical records will make it easier to understand which tests have been performed on your cancer and your test results.  It may be helpful to review your records with your doctor and ask these questions about biomarker tests:

• What is the purpose of the test?
• What type of sample is needed?
• Does my biomarker test result suggest that a type of treatment may work better for me?
• Does my biomarker test result suggest that I might have an inherited mutation? 
• Do any other biomarker tests provide additional information on how to best treat my cancer?

The following information may help you talk with your doctor about biomarkers and testing.

Purpose of the test

Biomarker tests may aid decision-making in different ways:

• Measuring risk for recurrence: Some tests predict how fast a cancer is growing and the risk for recurrence. Examples include OncotypeDX, Mammaprint and Endopredict for breast cancer and OncotypeDX and Prolaris for prostate cancer. 
• Monitoring response to treatment, progression or recurrence: These tests often measure changes in biomarkers over time to learn if the cancer is responding to treatment. Examples include CA125 testing to monitor ovarian cancer and PSA testing to monitor prostate cancer.
• Aiding in treatment selection: Some cancer treatments work best in people with certain biomarkers. In these cases, biomarker testing can help identify people who are most likely to respond to a particular treatment. 
• Detecting cancer:  “Liquid biopsies⁠” look for cancer cells or cancer cell DNA in the blood. These tests are also being studied to see if they can be used for early detection of cancer.  

Source of sample

• Some biomarker tests may be run on stored tumor tissue that was collected and saved at the time of your diagnosis, even if your biopsy was done a while ago. If you have enough tumor tissue stored, using this "archival tissue" may spare you from a new biopsy. 
• Some tests require fresh tissue, which means you may need a new biopsy. This is because some tumor biomarkers change over time as cancer cells grow, spread or become resistant to treatments. 
• Some cancer cells may release biomarkers into the blood, urine or other fluids. This provides a more convenient way to find cancer or to monitor response to treatment without the need for a tissue biopsy. Blood tests that look for abnormal cancer cell DNA are sometimes referred to as circulating tumor DNA tests, ctDNA or liquid biopsies. 

Biomarkers for treatment selection

Some targeted therapies and immunotherapies work best in cancers that have specific biomarkers. Biomarker tests may be used to select the best targeted therapy to treat a particular cancer. About 100 targeted therapies have FDA approval to treat different types of cancers. You can learn more about biomarker testing for treatment selection on our Cancer Treatment by Cancer Type and our Common Biomarkers sections.

Certain genes are important for repairing DNA damage. These are sometimes referred to as "DNA damage repair" (DDR) genes. Some therapies work best in cancers that have faulty DDR genes. You can read more about biomarker tests and treatments for these tumors in our DNA Damage Repair section.