Biomarker Testing for Cancer: What Patients Should Know

When a person is diagnosed with cancer, choosing the right treatment is one of the most important — and complex — decisions ahead. Biomarker testing is one tool that can help make that process more precise.

Also known as tumor testing, genomic profiling or molecular testing, biomarker testing looks for specific genes, proteins and other substances in cancer cells that can provide information about how a disease may respond to treatment, according to the National Cancer Institute (NCI).

What Is a Biomarker?

Every cancer has a unique pattern of biomarkers — genes, proteins and other substances found in cancer cells. Some of those biomarkers directly affect how certain treatments work. By identifying them, doctors may be better able to recommend therapies that are more likely to be effective for a specific person.

Biomarker testing is different from inherited genetic testing. Inherited mutations are passed down from parents and can increase a person's risk of developing cancer. Biomarker testing, on the other hand, focuses on changes that developed in a person's cancer cells during their lifetime — not changes they were born with.

How Biomarker Testing Can Guide Treatment

Biomarker testing is a central part of what is known as precision medicine — an approach that takes into account a person's genes, proteins and other biological factors when making care decisions.

Some targeted therapies and immunotherapies are only effective for people whose cancers have specific biomarkers. Identifying those markers can help a care team recommend treatments with a higher chance of working — and help patients avoid treatments that are unlikely to help.

Biomarker results can also open the door to clinical trials. Some studies enroll participants based on specific biomarkers rather than cancer type, an approach sometimes called basket trials. The NCI-MATCH and NCI-COG Pediatric MATCH studies, for example, use biomarker testing to match patients to treatments based on the genetic changes found in their cancers.

Who Should Consider Biomarker Testing?

Doctors generally recommend biomarker testing for people with cancer that has spread or returned after treatment, what is referred to as advanced cancer. It is also done routinely at diagnosis for certain cancer types, including non-small cell lung cancer, breast cancer and colorectal cancer.

The best first step is to talk with a health care provider about whether biomarker testing is right for an individual's care plan. It is also worth checking with a health insurance provider, as coverage can vary. Not every hospital offers biomarker testing, so patients may need to ask whether it is available through their current care team or if a referral is needed.

How the Test Is Done

For people with a solid tumor, a sample of cancer cells is typically collected during surgery or through a biopsy. For people with blood cancer — or for cases where a traditional biopsy is not safely possible — a liquid biopsy may be used instead. A liquid biopsy involves a blood draw and looks for biomarkers from cancer cells in the bloodstream.

The sample is then sent to a specialized lab, which analyzes it for biomarkers and creates a report. That report is reviewed with the patient's care team to determine next steps.

Types of Biomarker Tests

There are many types of biomarker tests available. Some check for a single biomarker, while others — called multigene tests or panel tests — check for many at once. One example is the Oncotype DX test, which looks at the activity of 21 different genes to help determine whether chemotherapy is likely to benefit someone with breast cancer.

Other tests analyze a cancer's total number of genetic changes, known as tumor mutational burden (TMB). A high TMB may indicate that a type of immunotherapy called immune checkpoint inhibitors could be effective.

For broader analysis, some tests use whole-exome sequencing, which examines all genes in a cancer, or whole-genome sequencing, which looks at all DNA in cancer cells.

The FDA has approved two liquid biopsy tests — Guardant360 CDx and FoundationOne Liquid CDx — which look in blood for biomarkers from cancer cells.

Understanding the Results

Biomarker test results can identify a treatment that may be effective, suggest that a certain therapy is unlikely to work or flag changes whose impact is not yet fully understood. In some cases, results may reveal genetic changes that appear harmless or fall into a category called "variant of unknown significance," which are generally not used to guide treatment decisions.

In some instances, results may point to a therapy that is FDA-approved for a different cancer type — an approach known as off-label use. This is because some treatments work based on the presence of a biomarker, regardless of where in the body the cancer started.

Results may also reveal inherited genetic changes, which could have implications for a patient's family members. If that occurs, a care team may recommend speaking with a genetic counselor to better understand what the findings mean.

When Biomarker Testing May Not Help

Biomarker testing does not benefit everyone. In some cases, a biopsy sample may not contain enough tissue for testing. In others, results may find no biomarkers that match available therapies. Even when a match is found, the treatment may not work — sometimes because not all cancer cells carry the same biomarkers, or because those biomarkers can change over time.

Because biomarker testing captures a snapshot of cancer cells at a specific point in time, results from a previous test may not reflect the current state of a person's cancer. A care team may recommend repeat testing if a cancer returns after treatment.

Coverage and Cost

The cost of biomarker testing varies depending on the type of test, cancer type and insurance plan. For people with advanced cancer, some biomarker tests are covered by Medicare and Medicaid. Private insurers often cover tests when there is sufficient evidence supporting their use in guiding treatment decisions.

Tests without that level of evidence may be considered experimental and may not be covered. If biomarker testing is part of a clinical trial a patient joins, the cost may be covered through the study. A study coordinator can provide more information.

For patients who want to explore open clinical trials that may match their biomarker results, NCI offers a clinical trials search tool at cancer.gov.

Reference

1. "Biomarker Testing for Cancer Treatment" by the National Cancer Institute — cancer.gov, updated December 2021.

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