A Complete Guide to Biomarker Headlines: Test, Target, Drug, and Evidence

Not every biomarker does the same job

HER2, EGFR, PD-L1, KRAS, MSI, NTRK, RET. These names run through treatment news as if they all worked the same way. They do not.

Some results select an approved treatment. Some estimate how a cancer is likely to behave. Some are only useful inside a research study. Telling them apart is most of the work of reading a biomarker headline well.

This page explains official sources. It is not medical advice and does not suggest a test or treatment.

What NCI means by biomarker testing

NCI describes biomarker testing as a way to look for genes, proteins, and other substances that give information about a cancer. Each person's cancer has its own pattern.

The same thing goes by many names: tumor testing, tumor profiling, genomic testing, molecular profiling, somatic testing, tumor subtyping. When a test is paired with one specific treatment, it may be called a companion diagnostic.

One distinction matters more than the vocabulary. NCI notes that biomarker testing is different from genetic testing that looks for inherited mutations you were born with. Tumor testing looks at the cancer. Inherited testing looks at you.

NCI's example of the payoff is EGFR. People whose cancer carries certain changes in the EGFR gene can receive treatments aimed at those changes. Our page on biomarker testing and precision medicine goes through the process.

A marker is not a verdict

NCI's tumor markers fact sheet is unusually candid, and it is the passage most headlines skip.

A tumor marker is anything present in or produced by cancer cells, or by other cells responding to cancer, or to certain noncancerous conditions. Because of that last part, NCI states that a raised level of a tumor marker does not mean someone has cancer. Noncancerous conditions can raise it.

The reverse is also true. Not everyone with a given cancer will have a raised level of the marker linked to it.

So NCI's guidance is that marker measurements are usually combined with other tests, such as biopsies and imaging, to reach a diagnosis. The pathology report is what provides the definitive cancer diagnosis, and it is also used for staging and planning treatment.

Where the sample came from changes the meaning

A marker can come from tumor tissue, from blood, from inherited DNA, from a protein stain, or from an imaging pattern. NCI notes that biomarkers are generally measured in tumor tissue, but tumors also shed cells and material into blood, which can be measured by tests called liquid biopsies.

Each method has its own limits, and the cutoff for calling a result positive can differ between laboratories. Two reports that both say positive may not mean the same thing.

What makes biomarker evidence trustworthy

Reliable evidence names four things up front: the test, the cutoff, the sample type, and the time point. Ideally the rule is fixed before it is checked in a separate group of people.

Be wary when researchers test many markers and report only the strongest link. That is how chance findings get published. And proving that selecting treatment by a marker actually helps people usually takes a clinical trial. NCI points to studies such as NCI-MATCH, which enroll people based on the biomarkers in their cancer rather than where the cancer started.

Common misreadings

• Finding a biomarker does not guarantee a matched drug will work.
• A drug approved for one cancer and biomarker pair may not be approved for another.
• Results from different laboratories and methods are not always interchangeable.
• "Biomarker-positive" on its own is an incomplete description. It leaves out the test, the sample, and the setting.

A responsible headline connects four parts: the exact test, the result, the cancer setting, and the evidence for one specific action. Targeted therapy only works when that chain holds.

Questions about a biomarker result

• What kind of biomarker is this, and how was it measured?
• Does it predict treatment benefit, or only describe risk?
• Is the linked treatment approved for this cancer and this stage?
• Would a different laboratory report the same result?

How this article was prepared

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. This page is for learning. It is not medical advice and does not suggest a test or treatment.

See an error, old source, or unclear wording? Tell us.