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What Is Biomarker Testing for Cancer Treatment?
You'll hear about biomarker testing, tumor profiling, and 'matching' treatments to a person's cancer. Here's what biomarker testing is and how it guides treatment choices.
A plain-language summary based on public reporting and trusted sources, linked below.
Please note: this page is educational only — it is not medical advice, and it does not speculate about anyone’s health beyond reliable public reporting. For questions about your own health, talk with your healthcare team.
What a biomarker is
NCI defines biomarker testing as a way to look for genes, proteins, and other substances — biomarkers, sometimes called tumor markers — that give information about a cancer. Every person's cancer has its own pattern of them.
Some of those biomarkers change how treatments work. That is why the test exists: not to name the cancer, but to help choose what to do about it.
The names it goes by
The same test appears under a confusing number of labels. NCI lists these as alternatives for the same thing:
- Tumor testing
- Tumor genetic testing
- Genomic testing, or genomic profiling
- Molecular testing, or molecular profiling
- Somatic testing
- Tumor subtyping
When a biomarker test is formally paired with one specific treatment, it is called a companion diagnostic.
The distinction that matters most
Biomarker testing is not the same as genetic testing for inherited cancer risk, and confusing the two causes real trouble.
Biomarker testing looks at the cancer. It examines changes that arose in the tumor itself during a person's life. Those changes are not inherited and are not passed to children. It is done for people who already have cancer.
Genetic testing for inherited risk looks at the person. It examines changes present in every cell from birth, inherited from a parent, which can be passed on and can affect relatives.
One guides treatment now. The other affects family screening and future risk. They answer different questions and often involve different clinics.
How the result gets used
Some treatments only work when a specific biomarker is present. NCI gives EGFR as an example: cancers with certain changes in the EGFR gene can be treated with EGFR inhibitors.
The 2011 FDA label for crizotinib shows how tight the link can be. The drug is indicated for non-small cell lung cancer that is ALK-positive "as detected by an FDA-approved test." Without that test result, the drug has no approved use — because without the genetic change it targets, it has nothing to act on.
This is what people mean by matching treatment to a cancer. Our page on targeted therapy explains how these drugs work, and our immunotherapy page covers the other main class where biomarkers guide selection.
Finding a trial
Biomarker results can also open a door to research. NCI describes basket trials, which enroll people based on the genetic changes in their cancer rather than where in the body it started — so a person with a rare mutation in an uncommon cancer may be eligible for a study alongside people with entirely different diagnoses.
NCI points to trials such as NCI-MATCH and NCI-COG Pediatric MATCH, which use biomarker tests to match people to treatments by the genetic changes in their cancers.
Where it falls short
NCI is unusually candid about the limits, and they are worth stating plainly.
- The test may find no biomarker that matches any available therapy.
- There may not be enough tumor tissue to run the test.
- A matched treatment may not be covered by insurance.
- Even when a biomarker matches a treatment, the treatment may not work.
That last one has a biological explanation. Not all of a person's cancer cells carry the same biomarkers, and biomarkers can change over time. A result describes the sample taken, on the day it was taken.
NCI also says directly that precision medicine is not yet part of routine care for most patients, and that the standard approach — choosing treatment by cancer type, size, and whether it has spread — is effective and is itself personalized.
Why results get repeated
Because a biomarker result is a snapshot, doctors sometimes retest. Common reasons include a cancer returning after treatment, a cancer progressing on a drug that had been working, or a new site of disease appearing that can be sampled.
A tumor under treatment pressure can evolve. Retesting is not a sign the first test failed.
When to raise this with your team
Biomarker testing is not automatic everywhere, and timing matters because results take time to come back. Ask about it:
- At diagnosis, before a treatment plan is finalized, particularly for lung, colorectal, breast, melanoma, and many advanced cancers.
- Before starting any targeted therapy or immunotherapy.
- If a treatment stops working and options are being reconsidered.
- If you are interested in clinical trials.
- If tissue was taken some time ago and circumstances have changed.
If you have symptoms and no diagnosis, biomarker testing is not the relevant step. Persistent, unexplained symptoms — bleeding, a lump that does not go away, unexplained weight loss, or a cough or hoarseness that lingers — need an assessment first. Our cancer treatment overview covers what follows a diagnosis.
What to keep in mind
- Biomarker testing is for people who have cancer. It is not a screening test and it is not inherited-risk testing.
- A result reflects the sample tested, at that time. It may not represent every cancer cell in the body.
- No matching treatment is a common and legitimate result, not a failure of the test.
- A biomarker match improves the odds that a treatment helps. It does not guarantee it.
- Nothing here is medical advice; whether testing belongs in your care is a decision for your team.
Questions to ask a healthcare team
- Should biomarker testing be part of my care, and is it available where I am treated?
- What would the results change about my treatment options?
- Is there enough tissue from my biopsy, or would another sample be needed?
- Could testing help me find a clinical trial?
- Will my insurance cover it, and how long will results take?
Sources
- National Cancer Institute, Biomarker Testing for Cancer Treatment: https://www.cancer.gov/about-cancer/treatment/types/biomarker-testing-cancer-treatment
- U.S. Food and Drug Administration, XALKORI (crizotinib) prescribing information, NDA 202570: https://www.accessdata.fda.gov/drugsatfda_docs/label/2011/202570s000lbl.pdf
How this page was made
An AI-assisted editorial system helped prepare this page. No named medical reviewer has reviewed it unless one is listed.
The National Cancer Information Foundation publishes Cancer Explained. It is not a diagnostic service, does not recommend treatments, and is not for emergencies.
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Put the story in context
Prevention, possible warning signs, screening, and diagnosis
This story relates to Biomarker testing. The information below is general: it does not reveal anything else about a public person’s health, and not every point applies to every cancer. Personal advice depends on age, symptoms, family history, exposures, and medical history.
Prevention and risk reduction
Not every cancer can be prevented. Avoiding tobacco, protecting skin from ultraviolet radiation, limiting alcohol, staying active, and receiving recommended HPV or hepatitis B vaccination can lower the risk of certain cancers. A risk factor is not a prediction or a cause in one individual.
Symptoms and possible early signs
Possible signs vary and are often caused by conditions other than cancer. Changes worth discussing include a new lump, unexplained bleeding or weight loss, a persistent cough, lasting bowel or bladder changes, a changing skin spot, or symptoms that persist or worsen. Some early cancers cause no symptoms.
Screening and early detection
Screening looks for certain cancers before symptoms begin. Recommended tests exist only for some cancers and depend on age and risk. Screening can have benefits and harms; it is not the same as evaluating a new symptom, and there is no single routine scan or blood test that reliably screens for every cancer.
How cancer is diagnosed
Diagnosis may involve a history and exam, imaging, laboratory tests, and often a biopsy. Pathology can identify the cancer type and may test biomarkers that guide treatment. Symptoms, screening results, tumor markers, or online stories alone cannot confirm cancer.
A public story may encourage questions, but it should not be used to estimate your risk or choose testing. Contact a healthcare professional about a persistent or concerning change. Seek urgent care for severe or rapidly worsening symptoms.