Cancer Treatment: What Are Biomarker Tests?

What are biomarkers?

Cancers are made up of abnormal cells. These cells can produce different types of abnormal substances, called biomarkers (or tumor markers). Biomarkers may be found within or around tumors, in blood, urine and other body fluids. They include: 

• proteins.
• genetic material (gene mutations, abnormal chromosomes, DNA or RNA, fused genes).
• cellular material.

What are biomarkers used for?

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:  Some biomarker tests are being studied to see if they can be used for early detection of cancer.  

What type of sample is needed for biomarker testing?

The type sample used for a biomarker test depends on the test being run. 

• Most biomarker tests are run on a piece of tissue from the tumor obtained by biopsy or surgery. 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 tumors may release cells or 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. These biomarker obtained from fluids are called liquid biopsies. 

What are liquid biopsies?

“Liquid biopsies⁠” are blood tests that look for cancer cells directly or evidence of cancer cells in the blood. There are different types of liquid biopsies. 

• Tests that look for cancer cells in the bloodstream are called Circulating Tumor Cell (CTC) tests. 
• Tests that look for DNA fragments from cancer cells are called circulating tumor DNA (ctDNA tests). 

Which biomarkers can be used for treatment selection?

Some therapies 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.