The short answer
An NTRK fusion is a biomarker result. It means a gene fusion involving an NTRK gene. In some cancers, biomarker results can help guide targeted therapy, immunotherapy, or clinical trial options, but the result only matters in context.
An NTRK fusion is a biomarker or molecular result, not a treatment decision by itself.
It can be relevant in rare subsets of many solid tumors.
A positive result may or may not change treatment depending on cancer type, stage, prior treatment, and available options.
Ask whether the result is from tumor testing, blood testing, inherited genetic testing, or another method.
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The full explanation.
The short answer
An NTRK fusion means part of an NTRK gene has broken off and joined a different gene. This creates one fused gene that makes an overactive growth protein. NTRK fusions are rare. But they can occur in many different cancers, in adults and in children alike. When one is present, it is usually the main driver behind the cancer's growth.
Where it may be relevant
This result can be relevant in rare subsets of many solid tumors. Not everyone with these cancers needs, or benefits from, the same testing or treatment.
Why it can affect treatment options
NTRK fusions are one of the clearest examples of treatment chosen by the biomarker, not by where the cancer started. Three pills — larotrectinib, entrectinib, and repotrectinib — are approved for advanced solid tumors with an NTRK fusion, when there is no good alternative treatment. Responses can be strong. Pooling three trials, larotrectinib shrank or cleared tumors in 75% of 55 people tested. Across three trials in adults, entrectinib did the same in 57% of 54 people; in children, it worked in 70% of 33 people. Repotrectinib, a newer drug designed partly to overcome resistance, shrank or cleared tumors in 58% of people who had not had a prior TRK inhibitor, and in 50% of those who had.
These approvals came through the FDA's accelerated pathway, so longer-term data are still being collected. This result points toward targeted therapy, not immunotherapy.
What this result does NOT tell you
A strong response rate in trials does not guarantee your cancer will respond, or respond for as long as someone else's did. Cancers can eventually develop resistance to a TRK inhibitor, which is part of why repotrectinib was developed as a next option. This result also does not tell you which cancer type you have — NTRK fusions cross many different cancers, so the fusion itself, not the original tumor type, guides treatment here.
Is this urgent?
An NTRK fusion result is not itself an emergency, but because it can open a strong, well-tolerated treatment option, it is usually worth acting on promptly once confirmed.
Questions to ask
Ask whether the fusion has been confirmed, and by which type of test. Ask which TRK inhibitor fits your situation and treatment history. Ask what monitoring looks like while on the drug, and what the plan is if resistance develops. Ask whether a clinical trial is relevant, given how much research is still ongoing in this area.
Sources
Words to know
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Common questions
What is an NTRK fusion?
An NTRK fusion means a gene fusion involving an NTRK gene. It is one type of result that may appear on a biomarker, molecular, genomic, or pathology report.
Can it affect treatment?
Sometimes. Certain biomarkers can point toward targeted therapy, immunotherapy, or a clinical trial, but the same result can mean different things in different cancers.
What should I ask my oncologist?
Ask whether the result is actionable for your cancer, whether a matched treatment exists, and whether a trial is relevant.
Questions to ask your doctor
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Sources last checked: 2026-07-30 what this meansLast updated: 2026-08-18Next planned review: 2027-07-30
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Editorial review complete — This page completed Cancer Explained's editorial checks (sources, safety, plain language, duplication). It has not been reviewed by a physician or other healthcare professional.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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