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IHC — immunohistochemistry — is the laboratory test on your biopsy that measures the key "markers" inside your breast cancer cells: the estrogen receptor (ER), the progesterone receptor (PR), the HER2 protein, and Ki-67. These results decide which treatments will work — hormone therapy, HER2-targeted therapy, or chemotherapy — and they define the breast cancer subtypes. This page explains what each marker means, how an equivocal HER2 result is settled with a FISH test, and why these numbers shape your whole plan. At CION, your first consultation is free.
Immunohistochemistry — usually shortened to IHC — is a special staining technique a pathologist uses on your biopsy tissue. It uses colour-tagged antibodies to detect specific proteins, or "markers", inside the cancer cells. For breast cancer, the markers that matter most are the estrogen receptor (ER), the progesterone receptor (PR), the HER2 protein, and Ki-67. The results are reported as part of your pathology report and form the basis of the entire treatment decision.
These same markers define the breast cancer subtypes you may have heard of — hormone-receptor-positive, HER2-positive, and triple-negative. In other words, your receptor status is not just a lab number; it is the single most important factor in deciding which treatments will help you.
IHC is run on the same tissue taken during your biopsy or surgery — no separate procedure is needed to measure ER, PR, HER2 and Ki-67.
The combination of ER, PR and HER2 results is what sorts breast cancer into hormone-positive, HER2-positive or triple-negative — each treated differently.
Receptor status tells your oncologist whether hormone therapy, HER2-targeted therapy or chemotherapy is the right backbone for you.
Your ER, PR and HER2 results are the single most important factor in choosing breast cancer treatment — more than the size of the tumour. They decide whether hormone (endocrine) therapy, HER2-targeted therapy or chemotherapy will help. That is why guidelines require ER, PR and HER2 testing on every invasive breast cancer, and why a borderline HER2 result is always rechecked with a FISH test before treatment is decided. Source: ASCO/CAP guidelines; NCCN Breast Cancer guidance.
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The estrogen receptor (ER) and progesterone receptor (PR) tell your team whether the cancer is fuelled by hormones. If a cancer is "hormone-receptor-positive", it is being driven by estrogen and/or progesterone — and that is good news, because it means hormone (endocrine) therapy, one of the most effective and best-tolerated treatments, will work against it.
Most breast cancers are ER-positive. The result is usually reported as a percentage of cells that stain positive, with a higher percentage generally meaning a stronger response to hormone therapy.
If positive, the cancer responds to anti-estrogen treatment. Hormone therapy such as tamoxifen or aromatase inhibitors can then block estrogen and slow or prevent the cancer.
The second hormone receptor checked. A PR-positive result supports the ER result and is also associated with a good response to hormone therapy.
ER and PR are scored by how many cancer cells stain positive. Even a low-positive result counts as positive and usually means hormone therapy should be considered.
Hormone-positive cancers can be treated with effective, well-tolerated tablets — see our hormone-receptor-positive page for what this means for your plan.
HER2 is a protein on the surface of breast cells that helps control growth. In some cancers there is far too much of it, which drives fast growth — these are called "HER2-positive". The crucial point is that HER2-positive cancers can be treated with HER2-targeted therapy (anti-HER2 antibodies), which has transformed the outlook for this once-aggressive subtype.
HER2 is first tested by IHC and scored 0, 1+, 2+ or 3+. A clear 0 or 1+ is negative and a clear 3+ is positive — but a 2+ result is "equivocal" and needs a confirming test.
HER2-negative. The cancer is not driven by excess HER2, so HER2-targeted therapy is not part of the standard plan. (Some "HER2-low" cancers in this range may have other options in the advanced setting.)
HER2-positive. There is clearly too much HER2, so HER2-targeted therapy is added to treatment. See our HER2-positive page for how these cancers are treated.
Borderline — the IHC cannot give a clear answer, so the result is confirmed with a FISH test (explained in the next section) before any HER2-targeted treatment is decided.
A HER2-positive result unlocks targeted therapy that specifically attacks the HER2 signal — getting this result right is therefore essential before treatment begins.
Two further tests round out the picture. FISH is used to settle a borderline (2+) HER2 result, and Ki-67 measures how fast the cancer is growing. Both add precision so that no treatment decision rests on an uncertain number.
FISH (fluorescence in-situ hybridisation) counts the actual HER2 gene copies in the cancer cells. It is more definitive than IHC and is the standard way to resolve an equivocal (2+) HER2 result.
Mainly for a HER2 IHC score of 2+. The FISH result then classifies the cancer as HER2-positive or HER2-negative, so the right treatment can be chosen with confidence.
Ki-67 is an IHC marker reported as a percentage of dividing cells. A higher value means faster growth — it complements the cancer's grade and can help decide whether chemotherapy is worthwhile.
ER, PR, HER2 and Ki-67 are read as a set, not in isolation. Together they define the subtype, estimate behaviour, and point to the right combination of treatments.
Because your receptor status decides your treatment, getting it right matters more than almost anything else in your report. CION ensures accurate ER, PR, HER2 and Ki-67 testing, confirms equivocal results with FISH, and has the whole panel interpreted by a tumour board — so your treatment is matched precisely to your cancer.
Trained at AIIMS, Tata Memorial, and leading international centres. Combined 150+ years of experience. Every complex case is reviewed by 3+ of them — together.
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
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MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
MBBS (AIIMS), MS (Surgery) (AIIMS), DNB (Surgical Oncology), MRCS (Edinburgh)
MBBS, MS(General Surgery), M.Ch(Surgical Oncology), FMAS, FARIS(Ongoing)
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The combination of ER, PR and HER2 sorts every breast cancer into a subtype, and the subtype determines the backbone of treatment. This is why two women with "breast cancer" can have completely different plans — their receptors are different. Understanding your subtype helps you understand your own treatment.
Each subtype below links to a detailed page, so you can read more about exactly what your receptor results mean for you.
The IHC section of a pathology report can look intimidating, but it follows a predictable pattern. Knowing what each line means helps you read your own report and ask better questions at your consultation. Remember that the interpretation — not just the numbers — is what matters, and that should always come from your oncologist.
For the bigger picture of where IHC fits in your overall workup, see our how breast cancer is diagnosed page.
Because your entire treatment hinges on these markers, an inaccurate or incomplete result can send treatment in the wrong direction. A cancer wrongly called HER2-negative might miss out on HER2-targeted therapy; a borderline result not confirmed by FISH leaves a decision on shaky ground. This is exactly why guidelines are strict about how ER, PR and HER2 are tested and reported.
If you have any doubt, a second pathology opinion is reasonable and routine. We support patients who want their receptor testing double-checked before committing to treatment.
"Tumour marker" can mean different things, and a few points often confuse patients. Here we clear up the most common ones so your report makes more sense.
The ER, PR, HER2 and Ki-67 discussed here are tissue markers, measured on the biopsy. They are different from blood "tumour markers" like CA 15-3, which are not used to diagnose breast cancer.
ER/PR-negative removes one treatment option, but HER2-negative is common and very treatable. Each result simply guides which therapy fits — none is a verdict on its own.
If a cancer returns or spreads, the markers may be re-checked on the new site, because receptor status can occasionally change — see our recurrence page.
Receptor status describes biology, not spread. How far the cancer has travelled is the stage, a separate part of your workup.
Your receptor results are the key to your treatment — they deserve to be tested accurately and read by experts. CION offers a clear, woman-led pathway from receptor testing to a matched treatment plan, with your first consultation free.
A specialist reviews your IHC report in full and explains what your ER, PR, HER2 and Ki-67 results mean for you — no rushed decisions, no unnecessary tests.
Where needed, we arrange a FISH test for equivocal HER2 or repeat testing — with up to 50% discounts on diagnostics — so your subtype is certain.
3+ oncologists read your markers alongside grade and stage, choosing hormone therapy, HER2-targeted therapy or chemotherapy as appropriate.
You receive a treatment plan built precisely around your receptor status, with whole-person support and transparent costs throughout.
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Start Your Story. Book Free Consultation.IHC stands for immunohistochemistry — a special staining technique a pathologist runs on your biopsy tissue. It uses colour-tagged antibodies to detect specific proteins, or "markers", inside the cancer cells. For breast cancer the key markers are the estrogen receptor (ER), the progesterone receptor (PR), the HER2 protein, and Ki-67. The results appear on your pathology report and are the foundation of your treatment decision, because they decide whether hormone therapy, HER2-targeted therapy or chemotherapy is the right backbone. IHC is run on the same tissue taken during your biopsy or surgery, so no extra procedure is needed.
ER (estrogen receptor) and PR (progesterone receptor) positive means the cancer is fuelled by these hormones — which is generally good news. It means hormone (endocrine) therapy, one of the most effective and best-tolerated breast cancer treatments, will work against it. These cancers are called hormone-receptor-positive and are the most common type. The result is usually given as a percentage of cells that stain positive; even a low-positive result counts as positive and usually means hormone therapy such as tamoxifen or an aromatase inhibitor should be considered. A higher percentage generally suggests a stronger response to hormone therapy.
HER2 is first tested by IHC and scored 0, 1+, 2+ or 3+, based on how strongly the cancer cells stain for the HER2 protein. A score of 0 or 1+ is HER2-negative, meaning the cancer is not driven by excess HER2. A score of 3+ is HER2-positive, meaning there is clearly too much HER2 and HER2-targeted therapy should be added. A score of 2+ is "equivocal" — the IHC cannot give a clear answer, so a FISH test is done to settle it. Getting the HER2 result right is essential, because it unlocks targeted therapy that specifically attacks the HER2 signal.
FISH stands for fluorescence in-situ hybridisation. It counts the actual number of HER2 gene copies in the cancer cells, which makes it more definitive than IHC. FISH is mainly used to resolve a borderline (2+) HER2 IHC result: it classifies the cancer as either HER2-positive or HER2-negative, so the right treatment can be chosen with confidence. This matters because HER2-targeted therapy should be given only to women who will truly benefit. At CION, an equivocal HER2 result is always confirmed with FISH before any HER2-targeted treatment decision is made.
Ki-67 is a marker measured by IHC and reported as a percentage — the proportion of cancer cells that are actively dividing. A higher value means faster-growing cancer. It complements the cancer’s grade, which also reflects how fast the cells divide. There is no single universal cut-off for "high" or "low" Ki-67, and laboratories can vary, so your oncologist interprets it alongside the grade, receptor status and the rest of the panel rather than as a standalone number. In some intermediate, hormone-positive cancers, Ki-67 can help decide whether chemotherapy adds enough benefit to be worthwhile.
No — this is a common confusion. The markers discussed here (ER, PR, HER2, Ki-67) are tissue markers, measured on the cancer cells from your biopsy, and they decide your treatment. Blood "tumour markers" such as CA 15-3 are different proteins measured in the bloodstream. Blood tumour markers are not used to diagnose breast cancer and are not reliable for screening; they are sometimes used to help monitor advanced disease, but even then they are interpreted cautiously alongside scans and symptoms. When people talk about the markers that decide breast cancer treatment, they mean the tissue receptors, not the blood tests.
Yes, occasionally. The receptor status of a breast cancer is usually stable, but it can sometimes differ between the original cancer and a recurrence or a site where it has spread. For this reason, if a cancer comes back or spreads, doctors may re-test ER, PR and HER2 on the new site, because the result could change which treatment is best. This is one of several reasons accurate, repeatable testing matters so much. At CION, receptor testing is repeated when clinically appropriate, and the tumour board uses the most relevant, up-to-date result to guide treatment.
Yes. CION offers a free first consultation for all cancer patients, including women who already have an IHC or pathology report and simply want to understand their ER, PR, HER2 and Ki-67 results. It is a full 45-minute consultation — a specialist reviews your report, explains what each marker means and what subtype it makes your cancer, and arranges a FISH test or repeat testing if needed, with up to 50% discounts on diagnostics. Your markers are interpreted by a tumour board alongside grade and stage, so the plan is matched precisely to your cancer. You can book on 1800-202-8726 or request a callback through the form on this page.
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