The short answer
Biomarker testing looks at the genes and proteins in a cancer to help choose treatments most likely to work. This approach, called precision medicine, can match people to targeted therapy or immunotherapy based on their tumor's specific features.
Biomarker testing examines the genes and proteins in a person's cancer.
It helps match people to treatments most likely to work for their specific tumor.
This approach is called precision medicine or personalized medicine.
Results can point to targeted therapy or immunotherapy options.
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The full explanation.
The simple version
Two cancers can look the same under a microscope and still be driven by different genes. Biomarker testing looks at the genes and proteins in a person's cancer. The results help pick the treatments most likely to work. That is the idea behind precision medicine.
How it works
A sample of the cancer is tested. It comes from a biopsy or from surgery. The lab looks for specific genes, proteins, or other markers. If it finds a change that a drug can target, that treatment may be an option.
Biomarker testing matches the treatment to the specific features of your cancer.
What it can point to
Results can point toward targeted therapy. Those are drugs aimed at a specific change in the cancer. Results can also point toward immunotherapy, which helps the immune system do the work. Matching treatment this way can make it work better. It can sometimes make it less toxic too.
Common biomarker words on reports
Reports use short labels for gene changes, protein scores, and DNA-repair patterns. Common examples include EGFR mutation, ALK rearrangement, KRAS G12C, and BRAF V600E. Others are PD-L1 TPS, PD-L1 CPS, MSI-H, dMMR, and TMB-high. You may also see NTRK fusion, HER2-low, HRD-positive, BRCA tumor mutation, PTEN loss, ESR1 mutation, and TP53 mutation.
Blood cancer and lab-method wording needs its own translation. Start with BCR-ABL, FISH testing, and flow cytometry. Then try bone marrow involvement, clonal hematopoiesis, and M-spike.
Did a new mutation or biomarker result appear in your portal? A focused question list is often the most useful next step, and the questions worth bringing are listed at the end of this page. The Question Builder turns them into something you can print.
Cancer-specific biomarker searches
The same biomarker can mean different things in different cancers. These pages tie the report language to the cancer context. Start with EGFR mutation in lung cancer, ALK-positive lung cancer, KRAS G12C in lung cancer, and KRAS G12C in colorectal cancer. Then see MSI-H colorectal cancer, dMMR endometrial cancer, BRCA mutation in ovarian cancer, and BRCA mutation in prostate cancer. Two more are HER2-low breast cancer and HRD-positive ovarian cancer.
Liquid biopsy and MRD wording
Blood-based tumor testing adds one more layer of report language. Start with circulating tumor DNA, tumor-informed ctDNA, and minimal residual disease. Then see molecular residual disease, Signatera, and Guardant360. Ask your team what a result means for you. Is it standard for your cancer? Is it investigational? Is it FDA-authorized for a specific use? Or is it part of a clinical trial?
Its limits
Not every cancer has a change that today's drugs can target. So testing does not always change treatment. But it is more and more a standard part of planning care, and the list of targetable markers keeps growing.
Words to know
Tap any term to see what it means.
Common questions
What is biomarker testing?
Biomarker testing looks at the genes, proteins, and other features of a person's cancer. Also called tumor or molecular testing, it helps doctors understand what is driving the cancer.
What is precision medicine?
Precision medicine means using information about a person's cancer — especially its biomarkers — to choose treatments most likely to help. It is also called personalized medicine.
How does it change treatment?
If testing finds a specific change, a targeted therapy or immunotherapy aimed at that change may be an option. This can make treatment more effective and sometimes less toxic than a one-size-fits-all approach.
Does every cancer have a biomarker to target?
No. Not every cancer has a change that current drugs can target. But testing is increasingly part of planning care, and options are growing.
Questions to ask your doctor
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Sources last checked: 2026-07-21 what this meansLast updated: 2026-08-11Next planned review: 2027-01-21
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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