Do I need testing before targeted therapy?

Usually yes. Most of the time your tumor has to be tested first, to prove it carries the specific target the drug is built to hit. Without that proof the drug has nothing to attack.

The test is called biomarker testing. It is also called tumor testing, tumor profiling, or somatic testing. All those names mean the same thing: a lab examines your cancer cells for genes, proteins, and other markers that a treatment could act on.

What the lab is actually looking for

Targeted drugs work on proteins that control how cancer cells grow, divide, and spread. So the question is narrow. Does your cancer carry that target or not?

The report you get back lists the biomarkers found in your cancer and any treatments that might match. A result may show a marker that a known therapy targets. It may show a marker that could keep a certain therapy from working. Or it may show changes thought to be harmless, which doctors generally do not use for treatment decisions.

When testing is not the gatekeeper

There are exceptions. In chronic myelogenous leukemia (CML), most people have a target for a certain drug.

Getting the sample, and what can go wrong

You may need a biopsy, a procedure in which a doctor removes a piece of the tumor. Biopsies carry risk, and the risk depends on how big the tumor is and where it sits. Your doctor should explain the specific risks for your tumor before you agree.

If you already had surgery, stored tissue from that operation can often be used, so ask before agreeing to a fresh biopsy. A liquid biopsy looks in blood or other fluids for biomarkers from cancer cells. Two liquid biopsy tests have FDA approval: Guardant360 CDx and FoundationOne Liquid CDx.

Several things can derail this. There may not be enough tumor tissue in the sample to run the test.

Biomarker testing is also not available at every hospital. Ask whether your center runs it in house or ships samples out, and ask how long results take, because that wait can shape when treatment starts.

Cost, and one thing worth doing

For people with advanced cancer, Medicare and Medicaid cover some biomarker tests. Private insurers often cover a test when there is solid evidence it is needed to guide treatment, Clinical trials that include biomarker testing might cover the cost, so ask the study coordinator.

One practical step: ask for a copy of your biomarker report and keep it. If your cancer returns, the markers may have changed and your doctor may retest, and having the earlier report makes the comparison possible.

Sources

https://www.cancer.gov/about-cancer/treatment/types/targeted-therapies

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