1800 202 8726
Breast cancer markers

HER2 FISH Testing: — Why the Second Test Is Ordered

If your HER2 report from the first test says 2+ or equivocal, your team has not finished testing. FISH is the follow-up that examines the gene directly and gives a definitive yes or no.

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

  • Not a repeat of the same test — FISH looks at the gene itself, not the protein on the cell surface. It uses different technology to give more precise information.
  • Ordered for one specific reason — FISH is only needed when IHC returns a 2+ equivocal score. A 0, 1+ or 3+ result does not need it.
  • It adds time and cost — FISH takes a few extra days and costs more than IHC. Knowing this in advance helps manage the wait.
  • The result guides treatment — Your oncologist needs a definitive HER2 result before deciding on a plan. FISH provides that certainty.
4.8 · 800+ Google reviews · 15,000+ patients treated
Limited Slots Today

Get this explained properly

₹950   Today: FREE  ·  Including free written second opinion

Reply within 2 working hours
Report reviewed by a senior oncologist
Confidential. No commitment to start treatment.
or
Call 1800 202 8726
17+
Cancer Specialists
on Panel
96.9%
Breast Cancer
Survival Rate*
15,000+
Patients
Treated
4.8★
Google Rating
(800+ reviews)

HER2 FISH testing is ordered when your first HER2 test (IHC) returns a 2+ equivocal result — borderline, neither clearly positive nor clearly negative. FISH examines the HER2 gene directly and counts gene copies to give a definitive answer. ASCO and CAP joint guidelines require reflex FISH for every IHC 2+ result before a treatment decision is made.

What do the terms on your HER2 report mean?

HER2
A gene that, when over-amplified, causes cancer cells to produce too many copies of a growth-promoting protein. Not every breast cancer has this change.
IHC (Immunohistochemistry)
The first HER2 test, done routinely on biopsy tissue. It measures HER2 protein on the cell surface and scores it 0, 1+, 2+ or 3+.
2+ / equivocal
A borderline IHC score — enough protein to stain, but not enough to call the result clearly positive or clearly negative. It is not a laboratory error; it identifies exactly the cases that need FISH to resolve.
FISH (Fluorescence In Situ Hybridisation)
A laboratory technique that uses fluorescent probes to count the actual number of HER2 gene copies inside each cell. It looks directly at the gene, not the protein.
Gene amplification
When a cell contains far more copies of a gene than normal. Amplified HER2 means the gene is producing an excessive amount of protein, which can drive tumour growth.
HER2-positive
The FISH result shows the HER2 gene is amplified. Your oncologist will factor this into your treatment plan.
HER2-negative
The FISH result shows the HER2 gene is not amplified. The equivocal IHC is resolved, and the plan will be based on your other markers instead.

How does FISH differ from the IHC test you already had?

FeatureIHC (first test)FISH (reflex test)
What it measuresHER2 protein on the cell surfaceHER2 gene copies inside the cell
TechnologyAntibody staining, light microscopeFluorescent probes, specialist microscope
Result formatScore: 0, 1+, 2+ or 3+Amplified or not amplified
When orderedRoutine — on all new breast biopsiesOnly when IHC returns a 2+ equivocal result
TurnaroundUsually 2–4 daysUsually several additional days on top of IHC
Certainty at 2+Borderline — cannot guide a decisionDefinitive in the large majority of cases

When does your team order FISH?

  • IHC score is 2+The standard trigger. ASCO and CAP guidelines require reflex FISH for every 2+ IHC result before any treatment decision.
  • IHC tissue quality was inadequateIf the biopsy sample did not process clearly enough for a readable IHC result, FISH may be ordered directly from the tissue block.
  • Second opinion requestedIf your case is reviewed at another centre, FISH may be repeated on the same tissue block to independently confirm the result.
  • Oncologist requests it for clinical reasonsRarely, FISH is ordered even when IHC shows 3+, if the clinical picture is unusual. Your team will explain if this applies to you.

Still unclear?

Send your reports across and a specialist will walk you through what they mean — what is known, what is not, and what the options actually are.

Meet the Specialists

17+ senior cancer specialists. One panel for your case.

Trained at AIIMS, Tata Memorial, and leading international centres. Combined 150+ years of experience. Every complex case is reviewed by 3+ of them — together.

Dr. Naresh Gundu
Medical Oncologist

Dr. Naresh Gundu

MBBS, DNB (Internal Medicine), DM (Medical Oncology)

View Profile
Dr. C. Raghavendra Reddy
Medical Oncologist

Dr. C. Raghavendra Reddy

MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)

View Profile
Dr. Bharati Devi Gorantla
Medical Oncologist

Dr. Bharati Devi Gorantla

MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)

View Profile
Dr. Owais Mohammed
Medical Oncologist

Dr. Owais Mohammed

MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)

View Profile
Dr. T. Raghavender Reddy
Medical Oncologist

Dr. T. Raghavender Reddy

MBBS, DM (Medical Oncology), MD (Radiation Oncology)

View Profile
Dr. N. Kiranmayee
Medical Oncologist

Dr. N. Kiranmayee

MBBS, DM (Medical Oncology), MD (Internal Medicine)

View Profile
Dr. Muralidhar Muddusetty
Surgical Oncologist

Dr. Muralidhar Muddusetty

MBBS (AIIMS), MS (Surgery) (AIIMS), DNB (Surgical Oncology), MRCS (Edinburgh)

View Profile
Dr. Raghavendra Naik
Surgical Oncologist

Dr. Raghavendra Naik

MBBS, MS (General Surgery), M.Ch (Surgical Oncology)

View Profile
Dr. Mohammed  Imaduddin
Surgical Oncologist

Dr. Mohammed Imaduddin

M.B.B.S, MS (General Surgery), M.Ch (Surgical Oncology)

View Profile
Dr. Vinay Mamidala
Surgical Oncologist

Dr. Vinay Mamidala

MBBS, MS(General Surgery), M.Ch(Surgical Oncology), FMAS, FARIS(Ongoing)

View Profile
Dr. Paila Gowri Naidu
Surgical Oncologist

Dr. Paila Gowri Naidu

MBBS, MS (General Surgery), M.Ch (Surgical Oncology), FMAS

View Profile
Dr. Venkata Sushma P
Radiation Oncologist

Dr. Venkata Sushma P

MBBS, MD (Radiation Oncology)

View Profile
Dr. Kirti Ranjan Mohanty
Radiation Oncologist

Dr. Kirti Ranjan Mohanty

MBBS, MD (Radiation Oncology)

View Profile
Dr. Gangadhar Vajrala
Radiation Oncologist

Dr. Gangadhar Vajrala

MBBS, MD (Radiation Oncology), MPH

View Profile
Dr. Basudev Pokhrel
Hematologist

Dr. Basudev Pokhrel

MBBS, M.D (Immunohematology & Blood Transfusion)

View Profile
Dr. Mohammed Imran
Interventional Radiologist

Dr. Mohammed Imran

View Profile
Dr. Vajja Sandeep Kumar
Surgical Oncologist

Dr. Vajja Sandeep Kumar

MBBS, MS (General Surgery), DrNB (Surgical Oncology), FALS Oncology

View Profile
Dr. Sridhar Kamani
Surgical Oncologist

Dr. Sridhar Kamani

MBBS, MS (General Surgery), DrNB (Surgical Oncology)

View Profile

Want a specific doctor for your case? Mention them when booking.

Book Free Consultation

Get a straight answer from a specialist

45 minutes, your reports reviewed, your questions answered in plain language.

Book Free Consultation Call 1800 202 8726

What does HER2 FISH testing cost, and why does it take longer?

FISH costs more than IHC because it uses specialised fluorescent probe kits, requires a different microscope, and needs trained staff to count signals manually inside each cell.

The cost varies by laboratory and by which probe system is used. Ask your hospital's pathology department for a current figure. Ask separately whether your insurance, Ayushman Bharat card, or state government scheme covers it — in many cases it does.

The extra days come from the FISH process itself and, at some centres, from sending 2+ samples to a referral laboratory with the specialist equipment. The wait is frustrating, but it does not mean something has gone wrong.

What else should you know about the FISH test?

What does a FISH-positive (amplified) result mean?

It means the HER2 gene is present in far higher numbers than normal in your tumour cells. Your oncologist will discuss what this means for your treatment plan in the context of your full report — including your ER, PR and Ki-67 results. An amplified result is a clear, actionable finding and your team will move quickly once they have it. Do not draw conclusions from the FISH result alone before speaking with your oncologist.

What does a FISH-negative (not amplified) result mean?

Your equivocal 2+ IHC result is resolved: the HER2 gene is not amplified. Your tumour is HER2-negative, and your oncologist will base the treatment plan on your other markers — ER, PR and Ki-67. A HER2-negative FISH result is not worse news; it means a different treatment path, not a worse one.

Can the FISH result also be borderline?

In most cases FISH gives a clear amplified or not-amplified answer. In a small number of cases the gene copy ratio falls close to the classification threshold and requires careful interpretation by a specialist pathologist. Current ASCO and CAP guidelines set out exactly how to handle these borderline cases. If your result is in this category, ask your team which specific group it falls into and what that means for next steps.

Will I need another biopsy for the FISH test?

No. FISH is done on additional sections cut from the same tissue block already taken during your biopsy. You do not need a new procedure. The only exception is if the original sample was very small and the laboratory determines there is not enough material left — your oncologist will tell you if that applies to you.

Why is FISH not done on everyone from the start?

IHC gives a clear answer in the large majority of cases — 0 and 1+ are clearly negative, 3+ is clearly positive. FISH is significantly more expensive and time-consuming. Running it on every sample would add cost and waiting time without changing the result for most patients. The two-step approach recommended by ASCO and CAP is the most efficient and accurate pathway overall.

What is the difference between FISH, CISH and ISH?

ISH (In Situ Hybridisation) is the general name for gene-counting tests. FISH uses fluorescent probes. CISH and DISH use different signal systems but examine the same thing — HER2 gene copy number. The term on your report depends on which system your laboratory uses. All of them give the same clinical information. If you are unsure which was run, ask your pathologist to confirm.

Did you know?

ASCO and the College of American Pathologists have updated their joint HER2 testing guidelines several times as laboratory science has evolved — including detailed guidance on how to classify borderline FISH results that do not fall neatly into amplified or not-amplified categories.

Across all those revisions, one requirement has stayed constant: a 2+ IHC result always needs a gene-level test before any treatment decision is made.

Source: ASCO/CAP HER2 Testing Guidelines in Breast Cancer

Explore 112 more Markers, Molecular Testing and Test Accuracy topics

HUB — How Accurate Is a Biopsy? Repeats, Errors and Second Opinions

HUB — IHC and Molecular Markers on a Biopsy

HUB — Labs, Slides and Second Opinions on a Biopsy

All Markers, Molecular Testing and Test Accuracy →

Next step

Still not sure what applies to you?

Send your reports across and a senior medical oncologist will go through what they mean, what is known, and what the options actually are.

Book Free Consultation Call 1800 202 8726
Common questions

Frequently asked questions

Why did my HER2 result come back as 2+ instead of positive or negative?

A 2+ IHC result means the HER2 protein level on the cell surface fell in a borderline range — enough to stain, but not enough to call clearly. This is not a laboratory error. The IHC test has a genuine grey zone at 2+, and identifying it correctly is the test doing exactly what it is designed to do. FISH exists specifically to resolve this group of results.

How long will I wait for my FISH result?

The FISH process itself usually adds several days to your IHC turnaround. If your centre sends 2+ samples to a specialist referral laboratory, add transit time on top of that. Ask your team when the sample was sent and what the expected return date is. Most centres can give a specific timeline. Waiting without a date is harder than waiting with one.

How much does HER2 FISH testing cost in India?

Cost varies by laboratory, city and probe system used, so there is no single reliable figure. Ask your pathology department or hospital billing team for a current quote before the test is sent. Ask separately whether your insurance, Ayushman Bharat card, or state government scheme covers it. Any figure you find online is indicative and may be several years out of date.

What happens after the FISH result comes back?

Your oncologist reads it alongside your full pathology report — ER, PR, Ki-67, tumour grade and stage. Together, these results give a complete biological picture of your specific tumour. Your oncologist will explain which results drive which parts of your treatment plan. It is reasonable to ask for the report in writing, as these conversations can be hard to remember clearly afterwards.

Can I ask my oncologist to proceed without the FISH test?

ASCO and CAP guidelines explicitly state that a 2+ IHC result is not sufficient to make a treatment decision on its own. The test exists because the 2+ group is genuinely split between positive and negative, and FISH resolves it definitively for patients on both sides. Treatment based on an unconfirmed result risks the wrong plan. FISH is a short additional wait that prevents that.

Does a HER2-negative FISH result mean my cancer is less serious?

No. HER2 status tells your oncologist which treatments are relevant for your tumour's biology — it is not a direct measure of how serious the disease is. Your overall picture depends on your full marker set, your stage and your grade, which your oncologist will interpret together. Ask your team to explain what each marker result means for your specific situation rather than drawing a conclusion from any single result.

Full index

Browse all 701 biopsy topics

Every page in this section, grouped by the part of the journey it belongs to. Pick a group to see what is in it.

What Is a Biopsy?

What Is a Biopsy? Everything You Need to Know →

Types of Biopsy Compared

Which Biopsy Will You Have? Techniques Compared →

Preparing for a Biopsy

What to Expect on the Day of Your Biopsy →

Recovery and Aftercare

After a Biopsy: Recovery, Aftercare and Warning Signs →

Biopsy by Body Part

Biopsy by Body Part: What to Expect at Each Site →

Understanding Your Report

How to Read a Biopsy Report: Terms Explained →

IHC and Molecular Markers

IHC and Molecular Markers on a Biopsy: What They Mean →

Grading and Scoring Systems

Cytology & Prostate Scoring Systems Explained →

How Accurate Is a Biopsy?

How Accurate Is a Biopsy? Errors and Second Opinions →

If Your Result Is Benign

Your Biopsy Is Benign: What It Means and What Comes Next →

Call now Book free consultation