Molecular & Genomic Testing

ALK and ROS1 Fusions in Lung Cancer: — Rare, Targetable, and Worth Finding

ALK and ROS1 are genetic fusions found in a small proportion of non-small cell lung cancers. They are rare — but they are among the most actionable findings in lung cancer medicine. Both are targetable, and finding either one reshapes the treatment plan entirely. Every person diagnosed with non-small cell lung cancer should be tested.

Medically reviewed by Dr. T. Raghavender Reddy, Medical Oncologist, MBBS · DM (Medical Oncology) · MD (Radiation Oncology) · Last reviewed September 2026

Rare but targetable — Fusions in ALK and ROS1 occur in a minority of lung cancers, but approved treatments exist specifically designed to block each one.
Not linked to smoking in the usual way — These fusions develop through a different mechanism from smoking-related damage. Smoking history is not a reason to skip the test.
Testing uses existing tissue — The biopsy you have already had is usually sufficient. A new procedure is only needed if that sample is too small or has degraded.
Missing this test has real consequences — If a fusion is present but not detected, the treatment plan is built on incomplete information. Current guidelines make testing a standard requirement, not an optional add-on.

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ALK and ROS1 are gene fusions found in a small proportion of non-small cell lung cancers. When either is present, it changes the treatment plan entirely. NCCN, ASCO and ESMO recommend testing everyone with non-small cell lung cancer, regardless of smoking history or stage.

What do ALK, ROS1 and fusion mean on your report?

Fusion gene: Two genes that should remain separate become joined together inside a cancer cell. The joined gene sends the cell growth signals it was never meant to receive, driving the cancer forward in a way that can be specifically targeted.
ALK (Anaplastic Lymphoma Kinase): A gene that, when fused with another, actively drives the growth of some lung cancers. When an ALK fusion is found, your oncologist can consider treatments designed specifically to block that signal rather than using a general approach.
ROS1: A separate gene that behaves similarly to ALK when a fusion occurs. ROS1 fusions are less common than ALK fusions but are equally important to detect — and equally targetable when found.
Driver alteration: A genetic change that is actively causing the cancer to grow. ALK and ROS1 fusions are driver alterations. Identifying the driver means treatment can be aimed at what is actually keeping the cancer alive.
Targetable: A driver alteration is targetable when approved treatments exist that are designed to block it specifically. Both ALK and ROS1 fusions are targetable, which is what makes finding them so significant.
NGS (Next Generation Sequencing): A laboratory method that reads many genes from your biopsy sample at once. It is the most comprehensive way to detect fusions alongside other driver alterations. NCCN, ASCO and ESMO recommend NGS over testing one gene at a time.
IHC (Immunohistochemistry): A faster, lower-cost test that detects the abnormal protein an ALK fusion produces. Often used as an initial screen. A positive or borderline result is followed up with a confirmatory test before any treatment decision is made.

Who should be tested for ALK and ROS1 fusions?

NCCN, ASCO and ESMO all recommend ALK and ROS1 testing for every patient diagnosed with non-small cell lung cancer, at the time of first diagnosis, regardless of age, stage or smoking history.

Fusions develop through a mechanism unrelated to smoking damage. They appear more often in people who have never smoked or smoked lightly — but they occur across the full range of patients. Smoking history is not a basis for skipping the test.

Testing is done on your existing biopsy tissue. If the sample is too small or has degraded, a liquid biopsy — a blood test that detects genetic material shed by the tumour — is an alternative, though tissue testing remains the more sensitive method.

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Ask your oncologist these questions if you are newly diagnosed

Has my tumour been tested for ALK and ROS1 fusions specifically?
Was NGS — comprehensive genomic profiling — done, or only individual gene tests?
Was the biopsy sample large enough for all recommended molecular tests?
When are the results expected, and how will I receive them?
If no fusions were found, which other driver alterations were tested for?
If the cancer progresses or spreads to a new site, should the testing be repeated?

Questions families often ask about fusion testing

Why test for something this rare? Is the cost justified?

Because the consequence of missing a targetable fusion is serious. A person with an ALK or ROS1 fusion who is not identified will receive a treatment plan that does not match their tumour biology. The test exists not despite the rarity but because of what finding it changes. NCCN, ASCO and ESMO all list it as a standard requirement, not an optional extra. Cost is a real concern — speak to your oncologist about which tests are covered under your hospital arrangement and which may need separate funding. Any figure you are given is indicative and should be confirmed with the laboratory directly.

How long does the result take?

IHC screening for ALK typically returns a result within a few days. NGS, which tests many genes at once, usually takes one to three weeks from when the sample reaches the laboratory. If your sample is being sent to a specialist laboratory outside your hospital, allow additional time for transit. Ask your team when the sample was dispatched and when the result is expected, so you are not waiting without a timeline.

What does a positive result actually mean for treatment?

A positive result means a targetable fusion has been found in your tumour. Your oncologist will discuss the treatment approach this makes available and how it compares to the alternatives for your specific situation — your stage, your overall fitness, and what else the molecular profile shows. A positive result is information the team needs to plan correctly. It does not by itself predict the outcome, but it means the plan is built on the right foundation.

My biopsy was done months ago. Do I need a new one?

Not necessarily. Fusion testing can be performed on stored biopsy tissue even if the procedure was done some time ago, provided the sample was fixed and preserved correctly. Your team will assess whether the existing sample is adequate. A new biopsy is only needed if the original sample is too small, has degraded, or was not processed in a way that permits molecular testing. If your cancer has progressed since the original biopsy, your oncologist may recommend testing a more recent sample regardless.

What if the result is negative for both ALK and ROS1?

A negative result means neither fusion was found in the sample tested — and that is the outcome for the majority of non-small cell lung cancer patients. It narrows the picture rather than closing it. Your oncologist will look at the full molecular profile, including other driver alterations and immune markers, each of which carries its own treatment implications. A negative result on two markers is not a dead end; it is direction toward the approach that is actually right for your tumour.

The laboratory says the biopsy sample is poor quality. What now?

Poor-quality samples are a recognised challenge in molecular testing. Your options depend on what the quality problem is. If the sample is too small, a repeat biopsy may be arranged from the primary tumour or a site the disease has spread to. If the issue is how the sample was processed, a liquid biopsy may provide a partial answer while a better sample is obtained. Ask your team to explain specifically what the quality issue is and what the plan is — a low-quality result should never be treated as a final negative without that conversation.

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Common questions

Frequently asked questions

Is ALK and ROS1 fusion testing different from a PD-L1 test?

Yes — they measure completely different things. PD-L1 testing looks at a protein on the surface of cancer cells that helps predict whether immunotherapy is likely to work. ALK and ROS1 testing looks inside the cell's DNA for gene fusions that are actively driving the cancer's growth. Both are standard tests for non-small cell lung cancer and give your oncologist different pieces of information. Ideally, they are done together — either as separate tests or through a comprehensive NGS panel.

Can fusion testing be done from a blood test alone?

Yes, through a liquid biopsy — a blood test that detects DNA fragments the tumour sheds into the bloodstream. It is a useful option when tissue is unavailable or insufficient. However, it is less sensitive than tissue testing and can sometimes miss a fusion that is present. For this reason, tissue testing is preferred when a sufficient sample exists. Your oncologist will weigh which approach is right for your situation.

My oncologist has not mentioned fusion testing. What should I do?

Ask directly at your next appointment whether ALK and ROS1 testing has been or will be arranged. Current guidelines from NCCN, ASCO and ESMO recommend it as a standard part of the workup for non-small cell lung cancer. If testing has not been discussed, ask why and whether it should be. You are entitled to a clear explanation of what has been done and what it showed. If you are uncertain after that conversation, seeking a second opinion at a centre with a dedicated lung cancer multidisciplinary team is a reasonable step.

My report says NGS was done. Does that include ALK and ROS1?

Usually yes — most NGS panels include ALK and ROS1 among the genes they test. However, the exact gene list varies between panels and laboratories, and not every panel is comprehensive. The safest way to confirm is to ask your oncologist or pathology team specifically which genes were included and what the results showed for ALK and ROS1. Do not assume that a panel being done means every relevant gene was covered.

Is fusion testing available at CION?

Molecular testing for ALK and ROS1 is coordinated as part of the diagnostic workup at CION centres. Your oncology team will determine which testing method is appropriate based on your biopsy sample and diagnosis — IHC screening, confirmatory testing, or comprehensive NGS. Imaging for treatment monitoring, such as PET-CT, is coordinated with partner imaging centres. If you have questions about where your sample is being sent and when results are expected, ask your CION oncology coordinator directly.

ROS1 fusions are described as very rare. Is it still worth testing?

Yes. The rarity is precisely why universal testing matters — there is no reliable way to identify from clinical features alone which patients have a ROS1 fusion. And because ROS1 fusions are targetable, missing one in a patient who has it carries real consequences for that person's treatment. NCCN, ASCO and ESMO all include ROS1 as a required test, not an optional one. Rarity does not reduce the importance of the result for the individual patient.

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