What Is Precision Medicine in Cancer?

A phrase that means something specific

"Precision medicine" and "personalized medicine" turn up in press releases often enough to sound like marketing. NCI gives them a plain definition.

Precision medicine is an approach in which prevention, diagnosis, and treatment are tailored to the genes, proteins, and other substances in your body. For cancer treatment, NCI says it means using biomarker and other tests to pick treatments most likely to help, while sparing you treatments unlikely to help.

Both halves of that sentence matter. Avoiding a drug that will not work is as much a result as finding one that will.

The test that makes it possible

Biomarker testing looks for genes, proteins, and other substances in a cancer that carry information about it. NCI notes that each person's cancer has its own pattern of these markers.

You will hear the same test called many things: tumor testing, tumor profiling, genomic testing, genomic profiling, molecular profiling, somatic testing, or tumor subtyping. When a test is paired with one specific treatment, it is called a companion diagnostic.

One distinction is worth holding onto. This is not the genetic testing that tells you about inherited risk. Biomarker testing looks at the cancer itself. Two people with the same type of cancer may not have the same changes in it, which is the whole reason to look.

Where the sample comes from

For a solid tumor, cells are usually taken during surgery. If there is no operation, a biopsy is done.

For blood cancers, or when a tumor cannot be reached safely with a needle, the sample is blood. NCI calls this a liquid biopsy, and names two that FDA has approved: Guardant360 CDx and FoundationOne Liquid CDx.

The sample goes to a specialized lab. The report that comes back lists the biomarkers found and any treatments that might match. Some gene tests also need a sample of healthy cells, usually blood, saliva, or a small piece of skin, so the lab can tell which changes belong to the cancer. Our page on biomarker testing walks through the report itself.

Three things a result can say

NCI sets out the possibilities honestly.

The result may show a biomarker that a known therapy targets. That therapy might be an FDA-approved option, an off-label use, or available through a clinical trial.

The result may show a biomarker that would stop a therapy from working. That spares you a treatment with side effects and no benefit.

Or, in many cases, the test finds changes that do not help with the decision at all. NCI says this plainly, and it is the outcome least often mentioned in headlines.

Some tests also measure tumor mutational burden, which can indicate whether immune checkpoint inhibitors might work. Our page on immunotherapy covers that class of drug.

What a large trial actually found

NCI-MATCH was built to test the whole idea. People with advanced solid tumors, lymphoma, or myeloma that had progressed on standard treatment, or with a rare cancer that had no standard treatment, had their tumors sequenced. If a genetic change matched one of the trial's treatment arms, they were assigned to it.

The trial enrolled 1,201 people across 38 arms. About 60 percent had cancers other than colon, rectal, breast, non-small cell lung, or prostate, which is the point: this approach is most valuable where there is no well-worn path.

NCI's summary of the result is measured. It says NCI-MATCH showed that people with advanced cancer may benefit from genomic sequencing to help plan treatment. Not that everyone benefits. Not that a match is always found.

Where it is already routine

For some cancers, this stopped being research years ago. HER2 testing decides treatment in breast cancer. EGFR and ALK testing shapes lung cancer treatment. BRAF testing guides melanoma treatment. In each case a test result, not the organ the cancer started in, picks the drug. Our overview of targeted therapy explains how those drugs work.

When to ask about it

Raise biomarker testing with your team if:

• you have advanced or metastatic cancer and are choosing between treatments.
• your cancer has progressed on a standard treatment.
• you have a rare cancer with no clearly established approach.
• you are considering a clinical trial, since many trials require a specific marker to enter.

Useful questions: has my tumor been tested, and for what? Would a broader panel change my options? Is there enough tissue left, or would I need another biopsy or a liquid biopsy? Is the test covered by my insurance?

What this does not mean

• Precision medicine is not a separate kind of treatment. It is a way of choosing among surgery, radiation, chemotherapy, targeted therapy, and immunotherapy.
• A biomarker test does not always change the plan. Often it finds nothing actionable.
• Finding a matching therapy does not guarantee it will work. It shifts the odds.
• This is not the same as testing for inherited cancer risk in a family. That is a different test with different implications.

Sources

• NCI: Biomarker Testing for Cancer Treatment
• NCI: NCI-MATCH Trial (Molecular Analysis for Therapy Choice)
• NCI: Targeted Therapy to Treat Cancer

How this page was made

An AI-assisted editorial system helped prepare this page. This article has not been reviewed by a healthcare professional unless a named reviewer is specifically shown. Cancer Explained is published by the National Cancer Information Foundation as a nonprofit-oriented public-interest education project. It is not a diagnostic service, does not recommend treatments, and is not for emergencies.

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