What is the difference between tumor testing and inherited genetic testing?

Tumor testing asks which drug might work on the cancer you have. Inherited genetic testing asks whether you were born with a change that raises your risk, and whether your relatives may carry it too. Same word, genetics, two completely different jobs.

The question each test is built to answer

Tumor testing, also called biomarker testing, tumor profiling, or somatic testing, examines the cancer cells themselves. The lab returns a report listing the biomarkers found and any treatments that might match. Three kinds of answer are possible. Your cancer may carry a target that a known drug hits. It may carry something that would make a certain drug fail. Or nothing useful turns up. That second answer is valuable too. It can spare you a treatment that would not have worked.

Sometimes a matching drug is approved for a different cancer that shares the same biomarker. Using it for your cancer is called off-label use, and it can be a real option.

Inherited testing, also called germline testing, examines healthy cells to find changes you have carried since birth. It does not pick your chemotherapy. It tells you three things. Whether your risk of certain cancers is raised. Whether you need earlier or more frequent screening. And whether your siblings and children should be tested.

What comes out of your body, and when

Tumor testing needs cancer cells. For a solid tumor, that means tissue taken during surgery or a separate biopsy. For blood cancers, or when a tumor is too risky to reach with a needle, a blood draw called a liquid biopsy can be used instead. Some gene-based tumor tests also ask for healthy cells, usually blood, saliva, or skin. The lab compares the two to see which changes arose during your life.

Inherited testing needs only healthy cells, so a blood tube or a saliva kit is enough. It can be done whether or not you have cancer.

Timing differs too. A tumor's biomarkers change over time, and a test is only a snapshot. If your cancer comes back after treatment, your doctor may want to test it again. An inherited result does not expire, though a variant can be reclassified as knowledge improves.

Reading the results without getting misled

Inherited testing has result categories that trip people up. A true negative means the specific change known in your family was not passed to you, so your risk is probably that of the general population. An uninformative negative means nothing was found, but your strong family history is still unexplained. You may still need extra checkups. A variant of uncertain significance, or VUS, means the lab found a change nobody yet knows how to interpret. Most VUS results are eventually reclassified as harmless, so a VUS is usually not used to make medical decisions.

The two tests can cross paths in one direction. A tumor test can pick up a change that looks inherited. That finding needs a separate germline test to confirm it before anyone acts on it. NCI advises talking with a genetic counselor, clinical geneticist, or certified genetic nurse when it happens. NCI also recommends genetic counseling before inherited testing, not just after.

Cost and access are not the same either

Tumor testing is not offered at every hospital, so ask whether your center does it or sends samples out. Coverage varies. For people with advanced cancer, Medicare and Medicaid cover some biomarker tests. Private insurers often pay when the evidence shows a test is needed to guide treatment. Tests without that evidence may be called experimental and denied. If you join a clinical trial that includes biomarker testing, the study may cover the cost, so ask the study coordinator.

A biomarker test can also fail you in ordinary ways. There may not be enough tissue in your sample, the matching drug may be off label and not covered, or the drug may simply not work in your body.

Sources

https://www.cancer.gov/about-cancer/treatment/types/biomarker-testing-cancer-treatment

https://www.cancer.gov/about-cancer/causes-prevention/genetics/genetic-testing-fact-sheet

https://www.cancer.gov/about-cancer/causes-prevention/genetics