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Lung cancer marker results

ALK and ROS1: — What These Lung Markers Mean

A lung cancer pathology report showing ALK or ROS1 can look alarming before you understand what the terms mean. Both are gene rearrangements — structural changes in tumour DNA — and, if present, they point toward a specific treatment class.

Medically reviewed by Dr. C. Raghavendra Reddy, Medical Oncologist, MBBS (Gold Medal) · DNB · DM (Medical Oncology, Gold Medal) · Last reviewed September 2026

  • Structural gene changes — ALK and ROS1 are gene rearrangements, not inherited mutations — they arise in the tumour itself.
  • Found in a minority — These rearrangements appear in a small proportion of non-small cell lung cancers, mainly adenocarcinoma.
  • Positive means targetable — A positive result points toward a treatment class that works differently from chemotherapy.
  • Confirmation may follow — IHC is often the first step; FISH or NGS may be ordered to confirm before treatment starts.
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ALK and ROS1 are gene rearrangements found in a small proportion of non-small cell lung cancers. Your IHC report shows whether the abnormal protein driven by either rearrangement is present in your tumour. A positive result means a class of targeted therapy may be relevant — your oncologist will advise on next steps and whether confirmatory testing is needed.

What do the terms in your report mean?

ALK rearrangement
A structural DNA change where the ALK gene has broken and rejoined with another gene, producing an abnormal protein that signals cancer cells to grow continuously.
ROS1 rearrangement
A similar structural change in the ROS1 gene. ROS1-positive tumours share biological features with ALK-positive tumours, and both carry a targetable alteration.
Gene fusion
Sections of DNA from two different chromosomes break and rejoin, creating a fused gene that produces a protein permanently switched on — which drives cancer growth.
IHC (immunohistochemistry)
A laboratory method that uses antibodies to detect specific proteins in tumour tissue. For ALK and ROS1, it shows whether the abnormal protein is present in the tumour cells.
Positive result
The abnormal protein was detected above the reporting threshold. A positive result does not mean the cancer is more dangerous — it means a specific treatment class may apply.
Negative result
The protein was not detected at a reportable level. Other markers tested alongside may still be relevant; ask your oncologist what the full panel showed.
FISH / NGS
Confirmatory tests used after a positive or inconclusive IHC. FISH detects the rearrangement at DNA level. NGS sequences many genes at once and can find rearrangements alongside mutations and other alterations.

Which patients are tested for ALK and ROS1?

These tests are recommended for non-small cell lung cancer — primarily the adenocarcinoma subtype. NCCN and ESMO guidance calls for reflex testing of all newly diagnosed non-squamous NSCLC for ALK and ROS1 alongside other key markers, meaning testing should happen at diagnosis rather than as a later step.

The rearrangements are more commonly found in people who have never smoked or smoked lightly, and in younger patients — but anyone with the right tumour histology may carry one regardless of age or smoking history.

What to do now that you have this result

  • Share the full pathology report with your oncologist — not a photograph of a summary page
  • Ask whether FISH or NGS is recommended to confirm the IHC result before treatment decisions are made
  • Ask which other targetable markers were tested at the same time — EGFR, KRAS, BRAF and others are separate
  • Ask what a positive or negative result means specifically for your cancer stage and histology
  • Tell your team everything you are currently taking, including supplements and traditional medicines

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What does a positive result mean for treatment?

A positive ALK or ROS1 result means a class of targeted therapy directed at that rearrangement may be relevant. These treatments block the abnormal protein rather than attacking dividing cells broadly — which is how they differ from chemotherapy.

Your oncologist will consider the result alongside your cancer stage, overall fitness and the outcome of any confirmatory testing before recommending a specific course. A positive IHC result opens a treatment pathway; the timing and details are decided with your team.

Questions families ask about these results

Can ALK and ROS1 both be positive at the same time?

Almost never. These are separate rearrangements and having both in the same tumour is exceptionally rare. If your report appears to show both positive, ask your oncologist whether confirmatory testing is recommended — one result may reflect a technical issue with the sample rather than a true double-positive finding.

My report gives a score or says 'weak positive' — what does that mean?

ALK IHC is often scored on a scale such as 0, 1+, 2+, 3+. Only scores above a validated threshold are considered positive for treatment purposes. The interpretation depends on which antibody and scoring system the laboratory used. Do not interpret the number alone — your oncologist reads it against the specific assay and the laboratory's reporting standards.

Does a negative result mean no targeted treatment is available?

A negative ALK or ROS1 result means those two rearrangements were not detected. It does not close off all targeted options. Other markers — EGFR mutations, MET alterations, KRAS, BRAF, RET, NTRK rearrangements — are tested separately, and any could still be relevant to your care. Ask your oncologist which markers have been tested and which are still pending.

The biopsy was done months ago — is the result still valid?

Yes, in almost all cases. IHC is performed on formalin-fixed tissue, which is stable over years when stored correctly. Results from an older biopsy are generally reliable for these markers. The exception is if your cancer has changed behaviour significantly since the biopsy — in that case your oncologist may recommend a repeat biopsy to reflect the tumour's current state.

What happens if the result was inconclusive?

IHC can give an indeterminate result when the biopsy sample was too small or not well preserved. In that case, FISH or NGS on existing or new tissue is typically the next step. An inconclusive result is a technical limitation of the sample, not a sign of anything unusual about your cancer, and it can usually be resolved with further testing.

Did you know?

NCCN and ESMO designate ALK and ROS1 as mandatory reflex markers — meaning testing should happen at the time of diagnosis for all eligible lung cancer histologies, not only after first-line treatment has failed.

Identifying a rearrangement early is what makes a targeted treatment pathway available from the outset of care.

Source: NCCN Clinical Practice Guidelines in Oncology — Non-Small Cell Lung Cancer; ESMO Clinical Practice Guidelines for Metastatic NSCLC

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Common questions

Frequently asked questions

What exactly is a gene rearrangement, and how is it different from a mutation?

A mutation is a change within one gene — a letter of the DNA code altered or deleted. A rearrangement is a larger structural event where a segment of one chromosome breaks and reattaches to another, creating a fused gene that did not exist before. ALK and ROS1 rearrangements are fusions of this kind. They arise in the tumour cells themselves and are not inherited — they are not passed to your children.

Does a positive ALK or ROS1 result mean my cancer is more aggressive?

Not necessarily. A positive result tells you something about the biology of the tumour — that it carries a rearrangement driving growth — but it is not a direct measure of aggressiveness. Prognosis depends on stage, performance status and response to treatment, not the marker alone. A positive result is most useful as a guide to which treatment class may apply to your care.

Should I ask for NGS even if my IHC result is already positive?

Your oncologist will advise based on local practice and your clinical situation. In some settings a strongly positive IHC is sufficient to proceed; in others, confirmatory FISH or NGS is standard before treatment begins. NGS also tests many other markers at the same time, which can be useful if the treatment plan needs to be reconsidered later. Ask your oncologist what they recommend for your case specifically.

How long does IHC testing for ALK and ROS1 take?

IHC results typically take a few days to one week from when the tissue sample reaches the laboratory, though turnaround times vary between centres. If you are waiting and have no timeline, ask your oncologist's team when the report is expected. A delay does not mean something is wrong — laboratories run tests in batches, and some samples require additional preparation steps before staining.

Can these rearrangements develop after the original treatment has started?

ALK and ROS1 rearrangements are generally present from the time of diagnosis — they are part of what drove the cancer's origin. It is uncommon for a new rearrangement to appear as a treatment resistance mechanism later, though tumour biology can change in other ways over time. If your cancer progresses, a repeat biopsy and re-testing may be recommended to see whether the molecular profile has shifted.

What should I bring to my appointment after receiving this result?

Bring the complete pathology report, not just a verbal summary or photograph of one page. Write down your key questions: which markers are positive or negative, whether confirmatory testing is planned, and what the treatment options are in order of priority. Also bring a full list of everything you are currently taking — supplements, herbal preparations and traditional medicines included — as some can interact with targeted treatments.

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