The short answer
A ROS1 fusion is a change in the ROS1 gene. NCI's lung cancer PDQ says ROS1 fusions are seen in up to 2% of non-small cell lung cancers. Targeted drugs called ROS1 inhibitors can treat these cancers.
ROS1 is a gene. A ROS1 fusion is a change in that gene found in some cancers.
A ROS1 fusion (or rearrangement) is a change in the structure of the gene.
It is seen in up to 2% of non-small cell lung cancers.
ROS1-positive cancers may be treated with targeted drugs called ROS1 inhibitors.
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The short version
ROS1 is a gene. In some cancers, part of the ROS1 gene joins with part of another gene. This is called a fusion or rearrangement. A cancer with this change is called ROS1-positive.
Where it is found
NCI's lung cancer treatment summary says ROS1 fusions are seen in up to 2% of non-small cell lung cancers.
Why it matters for treatment
The same summary says these cancers respond to targeted drugs called ROS1 inhibitors, such as crizotinib and entrectinib. Treatment choices depend on many things, so your care team will explain what fits you.
A tumor finding
A ROS1 fusion is found by testing the cancer. Ask which sample was tested.
What to ask
Ask how your result changes your options, whether other changes were tested, and whether a clinical trial could fit. Your oncologist can explain what your result means for your plan.
Sources
Common questions
What does ROS1-positive mean?
ROS1-positive describes cancer cells with a ROS1 gene fusion or rearrangement. Ask your care team how it affects your plan.
How common is it?
NCI's lung cancer treatment summary says ROS1 fusions are seen in up to 2% of non-small cell lung cancers.
How is it treated?
NCI's lung cancer PDQ says ROS1 fusions respond to targeted drugs called ROS1 inhibitors, such as crizotinib and entrectinib. Your care team will explain which options fit your situation.
Is a ROS1 fusion inherited?
A ROS1 fusion is a change found in the tumor. Ask your care team whether your test looked at the tumor or at your inherited genes.
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Sources last checked: 2026-10-02 what this meansLast updated: 2026-10-02Next planned review: 2027-09-27
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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, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
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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