What are cancer biomarkers and what is biomarker testing?

What are biomarkers?

Biomarkers are measurable signs, such as genes, proteins, or other substances, found in the body that give clues on how cells and tissues are working. They can be found in tissue or body fluid samples. In cancer, specifically, biomarkers are signs produced by cancer cells themselves or by your body in response to cancer.

What is biomarker testing?

Biomarker testing is done using a tissue and/or liquid biopsy. A tissue biopsy requires a procedure to collect a small sample of tumor tissue. Liquid biopsy collects a sample of blood or another body fluid, such as saliva or urine. The type of test your doctor may recommend depends on your cancer type and the specific biomarkers they are looking for.

Biomarkers can provide a variety of information. For example, prognostic biomarkers show how your cancer might behave, such as how fast it may grow and the chance of it coming back. Predictive biomarkers can show how your cancer is likely to respond or not respond to certain treatment plans, which can help your doctor choose the therapies better suited for you. You can learn more about the different classifications or types of biomarkers by reading The importance of biomarker testing.

The type of biomarker testing recommended can depend on your specific diagnosis, so it’s always a good idea to talk with your care team about which tests are best for you. You can use this discussion guide to prepare for your conversation with your doctor.

In a cancer journey, biomarker testing may also be called:

• companion diagnostic testing (when paired with a specific treatment)
• genomic testing or genomic profiling
• molecular testing or molecular profiling
• somatic testing
• tumor subtyping
• tumor testing
• tumor genetic testing

Unlike routine bloodwork, biomarker testing is not about your general health. Instead, it is specifically designed to uncover information about your cancer. It does not replace the standard lab tests you may already be familiar with. To learn more about biomarkers in cancer care and how they may help guide your treatment plan, visit the National Cancer Institute’s list of tumor markers. Please note that as cancer research continues, additional biomarkers may be identified over time.

Many people find it confusing to keep track of all the different tests used in cancer care. Genetic testing and biomarker testing may sound similar, but they are not the same. While genetic testing looks for inherited changes in your DNA, biomarker testing looks at the cancer itself, including what it’s made of and how it behaves. Depending on the type of cancer, biomarker testing may examine:

• Proteins such as HER2 in breast cancer or PD-L1 in non-small cell lung cancer
• Metabolic changes that show how cancer cells use energy or glucose
• Other substances including circulating tumor DNA or fragments of RNA

Interpreting biomarker test results

Interpreting results is truly a team effort. Your doctor helps decide which tests are needed, pathologists carefully perform and confirm the results, and genetic counselors help determine if the findings could affect your family members, and if additional genetic testing is recommended. Together, this team uses your biomarker information to create a care plan tailored to you. To help you prepare for your next conversation with your care team, read How to talk to your doctor about biomarker testing.

How biomarker testing can help shape your treatment plan

If actionable biomarkers are found, they can help doctors determine which treatment options may be more or less likely to work for you.

Limitations of biomarker testing

Like all medical tests, biomarker tests are not perfect. A false positive suggests a biomarker is present when it isn’t, while a false negative misses a biomarker that is there. Such false readings or results can occur if the tumor sample is too small; the cancer has changed over time, or if the test technology has limits.

It’s also important to know that liquid biopsies are generally less sensitive than tissue biopsies, meaning they are more likely to miss certain biomarkers. For this reason, if a liquid biopsy comes back negative, your doctor may order a tissue biopsy to confirm results, as tissue biopsy is considered the gold standard.

While biomarker testing can provide valuable information, it is not absolute. It serves as a tool, along with imaging, pathology, and your overall health, to guide treatment decisions.

Biomarker information for your family

Some biomarker findings can suggest a hereditary (inherited) cancer risk. If your results point to an inherited cancer risk that may affect family members, your care team may recommend meeting with a genetic counselor. They can help your relatives decide whether they should be tested, explain insurance coverage, and assist with scheduling testing—often through a blood or saliva test. Identifying inherited risks early allows family members to take preventive steps and stay on top of recommended screenings.

Ordering biomarker testing

It’s ok to be proactive and ask your doctor about biomarker testing and whether it’s right for you. Your oncologist can help determine what testing is appropriate based on your diagnosis, treatment goals, and overall health. Read How to talk to your doctor about biomarker testing for tips on preparing questions and understanding what to expect.