Cancer Drug Approvals: How Companion Diagnostics Shape

What did the review find about cancer drug approvals?

The review examined public FDA records for drugs associated with companion diagnostic tests. Among the 62 solid-tumor medicines, 16 had efficacy datasets involving fewer than 100 patients. These figures describe the evidence used to establish efficacy in the reviewed approval settings; they should not be interpreted as the total number of people ever exposed to each medicine. [Frontiers in Medicine review](https://www.frontiersin.org/journals/medicine/articles/10.3389/fmed.2026.1938709/full).

This was a descriptive analysis of regulatory records, rather than a clinical trial comparing treatments. It therefore cannot establish that diagnostic-guided development itself caused smaller studies or that the resulting medicines are less safe. Its findings point to a practical question for interpreting approvals: how much uncertainty remains after a treatment becomes available?

How do companion diagnostics help match patients to cancer drugs?

The FDA defines companion diagnostics by their essential role in using a corresponding treatment safely and effectively. Depending on the test, they can identify patients more likely to benefit, flag elevated risks of serious adverse effects, or help monitor treatment response. Test accuracy matters because an incorrect result can lead to an inappropriate treatment decision. [FDA companion diagnostics overview](https://www.fda.gov/medical-devices/in-vitro-diagnostics/companion-diagnostics).

A concrete example is testing a tumor for particular EGFR gene changes that can guide the use of EGFR inhibitors. Selecting patients whose cancers carry a relevant target gives researchers a biologically focused population in which to evaluate a medicine. However, a matching result does not guarantee success: tumors can contain different cell populations, and their biomarkers can change over time. [National Cancer Institute biomarker testing guide](https://www.cancer.gov/about-cancer/treatment/types/biomarker-testing-cancer-treatment).

What should patients ask about evidence behind a targeted treatment?

One useful distinction is between evidence that a tumor shrinks and evidence that a treatment improves how long or how well people live. Under accelerated approval, the FDA may authorize a medicine for a serious condition with unmet need using a surrogate endpoint expected to predict clinical benefit. Companies must then conduct studies to confirm that benefit; unsuccessful confirmation can lead to withdrawal. This pathway does not apply automatically to every targeted cancer medicine. [FDA accelerated approval program](https://www.fda.gov/drugs/nda-and-bla-approvals/accelerated-approval-program).

For an individual treatment decision, the practical implication is to discuss the evidence alongside the exact biomarker result, cancer type, previous treatments and available alternatives. Patients can ask whether the proposed treatment is approved for their situation, would be used off label, or is available through a clinical trial. Those are different routes to care, and a biomarker report may identify possibilities in any of them. [National Cancer Institute biomarker testing guide](https://www.cancer.gov/about-cancer/treatment/types/biomarker-testing-cancer-treatment).