IHC Markers Explained

What If the IHC Panel — Is Inconclusive?

An inconclusive IHC result is not a failed test. It means the staining pattern landed in a range the pathologist cannot call without more information. There are clear next steps, and most equivocal results are resolved before treatment needs to begin.

Medically reviewed by Dr. Muralidhar Muddusetty, Surgical Oncologist, MBBS (AIIMS) · MS Surgery (AIIMS) · DNB Surg Onc · MRCS (Edinburgh) · Last reviewed September 2026

Not a lab error — Equivocal results are a recognised limitation of IHC — they occur with certain markers at borderline staining intensities.
A defined path forward exists — A follow-up test — often a repeat IHC or FISH — is ordered to clarify what the staining alone could not.
May or may not affect timing — Whether it delays your treatment depends on which marker is equivocal and how central it is to the next decision.
Your team decides the next step — The choice of follow-up test is made by the pathologist, guided by the specific marker in question.

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An inconclusive IHC result means the staining pattern fell in a range where your pathologist cannot call it clearly positive or negative. This is a recognised technical limitation, not a failure. Most cases are resolved by repeating the test, adjusting the method, or switching to a complementary technique such as FISH or molecular testing.

What do the terms on an inconclusive report mean?

Equivocal: A result that falls between clearly positive and clearly negative. The pathologist cannot make a definitive call from the IHC staining alone.
2+ score: A borderline IHC score used for certain markers. It means the result is ambiguous and a DNA-based test is needed to resolve it.
Heterogeneous staining: When different cells in the same tumour stain at different intensities. It makes a single categorical call unreliable.
Pre-analytical variables: Conditions before the staining begins — how quickly tissue was fixed after biopsy, the fixative used, how long it was processed — that directly affect the quality of the result.
Reflex testing: A follow-up test automatically ordered when an IHC result meets a defined borderline threshold. It is a planned step in the protocol, not a sign that something went wrong.
FISH / ISH: DNA-based tests that count gene copies rather than read protein expression. Used to confirm or rule out what an equivocal IHC result could not settle on its own.

What does the pathologist do after an inconclusive result?

Reviews the original stained slides again before ordering anything new.
Checks tissue fixation time and processing records to identify any technical cause.
Repeats the IHC stain on a new section from the same tissue block.
May try a different antibody clone if the first produced inconsistent staining.
Orders FISH or ISH testing when the marker's protocol specifies it for borderline scores.
Cuts deeper sections if the tumour area on the original slide was too small to read.
Requests a new biopsy only if the tissue block has been exhausted.

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Does an inconclusive result delay your treatment?

It depends on which marker is equivocal. For some markers, the result informs treatment choice but does not hold it up. For others, the marker directly decides which pathway is recommended — and your team will wait for a resolved result before proceeding.

Most equivocal results are clarified within days to a few weeks, provided tissue is available and the follow-up test is ordered without delay. Ask your oncologist directly: which marker is inconclusive, and does resolving it affect when your first treatment can begin.

Questions families ask about inconclusive IHC

Why did the staining come out unclear?

IHC measures protein expression by how deeply a stain binds to cancer cells. The problem arises in the middle range — not deeply stained, not unstained — where intensity alone cannot answer the question. Tissue that was not fixed quickly after biopsy, or that was over-processed, can also produce weak or patchy staining. Neither is a mistake; they are known limitations the protocol is designed to catch and address.

Can the same tissue block be tested again?

Usually yes. The original biopsy block is held in the pathology department and can be sectioned again for a repeat IHC or a FISH test. The block is a physical archive that can be used for multiple tests and sent between hospitals for second opinions. If the block is exhausted, a new biopsy may be needed — your pathologist will tell you if that applies.

What is FISH testing and is it better than IHC?

FISH looks at the DNA inside cancer cells to count gene copies, rather than reading the protein that gene produces. It answers a different question from IHC, not a better one — the two tests complement each other. For certain markers, guidelines from ASCO and CAP specify that an equivocal IHC should be followed by ISH testing. That is because the borderline zone is exactly where the DNA count adds clarity the staining cannot provide.

Does an inconclusive result mean my cancer is harder to treat?

No. An inconclusive IHC result is a statement about the test, not the cancer. Once the follow-up test resolves the result, your team proceeds with exactly the same decisions they would have made with a clear result from the start. Being in the equivocal zone does not change what the cancer is — it delays knowing which category it falls into, and that is what further testing resolves.

Should we ask for a second pathology opinion?

Yes, and it is a well-accepted step in oncology for borderline results. Most cancer centres can arrange for slides or the tissue block to be sent to another laboratory. It is not a sign of distrust — pathology interpretation involves professional judgement, and a second opinion on an ambiguous result is standard practice. Your oncologist can coordinate it, and it is reasonable to ask if the equivocal marker is central to your treatment decision.

What if the follow-up test is also inconclusive?

This is uncommon but can happen when a tumour has genuinely borderline biology. When both IHC and ISH are equivocal, the case moves to a multidisciplinary team discussion — oncologists and pathologists reviewing the full picture together. Recommendations in these cases are guided by the clinical context and the available evidence, not the marker result alone. Your oncologist will explain what the team concluded and why.

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Common questions

Frequently asked questions

What does 'equivocal' mean on a pathology report?

Equivocal means the staining fell between clearly positive and clearly negative. The pathologist cannot make a reliable call from the IHC alone. It does not mean the test was done incorrectly — it means the result landed in a zone where a second test is needed to resolve it. That is an expected situation with certain markers, and the protocol anticipates it.

How long does it take to get a resolved result after an inconclusive IHC?

Most follow-up tests are completed within days to a few weeks, depending on what is ordered and whether the block is at the same laboratory or needs to be retrieved. Ask the pathology team when the sample was sent and when the result is expected, so you have a concrete timeline rather than an open-ended wait.

Does an inconclusive result mean the tissue sample was poor quality?

Sometimes, but not always. Tissue quality does affect staining, and a poorly fixed or very small sample can produce an unreadable result. More often, the tissue was adequate but the staining landed in a borderline zone that genuinely needs a second test. Your pathologist will note in the report if sample quality was the issue.

Will I need another biopsy?

Usually not. Most equivocal results are resolved using the existing tissue block — by cutting a new section or running a different test on the same material. A new biopsy is only needed if the block has been used up or the original sample was too small. Your pathologist will tell you directly if that is the case.

Does an inconclusive IHC mean my cancer is unusual?

Not necessarily. Equivocal results occur in a proportion of cases for certain markers, and the protocol anticipates them — that is why reflex testing exists. Some tumours do have genuinely borderline biology, but many equivocal results resolve cleanly with the follow-up test. An inconclusive result on one marker does not affect how the rest of your diagnosis is interpreted.

Who decides what test comes next?

The pathologist makes that decision, guided by the specific marker in question. For certain markers, the follow-up test is defined in guidelines from ASCO and CAP, so it is not a matter of individual preference. Your oncologist will explain which marker is equivocal and what the follow-up test is expected to establish.

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