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Reading your pathology report

Which IHC Markers Matter — for Your Cancer Type

When you look at a pathology report and see a column of abbreviations with plus and minus signs, you are reading an IHC panel. The markers tested differ by cancer type. This page maps which ones are standard for each type and what each one is looking for.

Medically reviewed by Dr. Bharati Devi Gorantla, Medical Oncologist, MBBS · MD · DM (Adyar, Chennai) · ECMO · MRCP SCE (UK) · Last reviewed September 2026

  • Different panels for different cancers — A breast cancer panel and a lymphoma panel test completely different proteins.
  • Some markers are essential — An incomplete panel can leave your oncologist without information needed to decide next steps.
  • 2+ is not a final HER2 result — A borderline score of 2+ requires a follow-up FISH or CISH test before a conclusion is drawn.
  • The full panel is what matters — Your oncologist reads all the markers together — single results without context can mislead.
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Each cancer type has a standard IHC panel — the set of protein markers that confirm the diagnosis and guide next steps. Breast cancer always includes ER, PR, HER2, and Ki-67. Lung cancer panels typically include TTF-1 and PD-L1. Colon cancer panels include CDX2, CK20, and MMR markers. Your oncologist interprets the full panel, not individual results.

What do the abbreviations on your IHC report mean?

IHC (Immunohistochemistry)
A laboratory staining test that uses antibodies to detect specific proteins on tumour cells. A plus sign (+) means the protein was found. A minus sign (−) means it was not detected.
ER (Oestrogen Receptor)
A protein found on some breast cancer cells that responds to oestrogen. Reported as positive or negative, with a percentage showing how many cells carry it.
PR (Progesterone Receptor)
A protein similar to ER, also tested in every breast cancer panel. Reported alongside ER as positive or negative.
HER2
A growth-promoting protein scored from 0 to 3+. A score of 3+ is strongly positive. A score of 2+ is borderline and requires a follow-up FISH or CISH test to clarify.
Ki-67
A measure of how quickly tumour cells are dividing. Reported as a percentage of cells actively growing. Your oncologist uses it to assess how fast the tumour is behaving.
TTF-1
A marker used to confirm whether a lung tumour started in the lung or spread there from elsewhere. Also seen in some thyroid cancers.
CDX2
A marker linked to gut-type cells. A positive result suggests the cancer started in the colon, rectum, or small bowel.
MMR markers (MLH1, MSH2, MSH6, PMS2)
Four proteins that show whether the cancer's DNA repair system is working. A loss in any one is called dMMR, or mismatch repair deficiency. This result appears on colon, stomach, and some other cancer panels.

What to confirm before your next appointment

  • Ask whether the panel is complete for your cancer type — your oncologist can confirm this.
  • If HER2 came back 2+, confirm whether a FISH or CISH test has been requested.
  • Check that the MMR panel was included if you have colon or stomach cancer.
  • Keep a copy of the full pathology report for second opinions or referrals to another centre.
  • Ask your oncologist what the full panel means for your treatment plan.

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Why do different cancers need different IHC markers?

Each cancer type expresses a characteristic set of proteins. Pathologists use IHC to confirm where the cancer started and what type of cell it came from — particularly when a tumour is found somewhere that could be either a primary cancer or a spread from another site.

Some markers are essential for a given cancer type and the panel is incomplete without them. Others are added when the diagnosis is uncertain. The table below maps the standard panel for the most common cancers seen in India.

Which IHC markers are standard by cancer type?

Cancer typeEssential markersAlso commonly tested
BreastER, PR, HER2, Ki-67p53, E-cadherin (for lobular subtype)
LungTTF-1, CK7, Napsin-APD-L1, p40 (squamous type)
Colon / RectumCDX2, CK20, MMR panel (MLH1, MSH2, MSH6, PMS2)CK7 (to exclude other primary sites)
Stomach / GastricHER2, MMR panelPD-L1, CK7, CDX2
Lymphoma (B-cell)CD20, CD3, CD45, Ki-67BCL2, BCL6, MYC (for subtyping)
LiverHepPar-1, GPC3CK7, CK20 (to distinguish from bowel or bile duct spread)
Cervixp16, p63CK7, Ki-67
ProstatePSA, PSAP, NKX3.1p63, CK5/6 (high-grade confirmation)
ThyroidTTF-1, ThyroglobulinCalcitonin (medullary type), Ki-67

Did you know?

A biopsy sample and a surgical specimen from the same patient sometimes show different HER2 scores. ASCO and CAP guidelines note that a change between the two should be discussed with your oncologist — the result from the larger surgical sample is generally considered more representative of the tumour overall.

If your score has changed between two reports, ask your team which result is being used and why.

Source: ASCO/CAP HER2 Testing Guidelines for Breast Cancer

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Common questions

Frequently asked questions

What does a plus or minus sign next to a marker mean?

A plus sign (+) means that protein was found on the tumour cells. A minus sign (−) means it was not detected. Some markers, like HER2, use a numbered score rather than a simple plus or minus because the strength of the signal also matters. A high score is not automatically worse and a low score is not automatically better — what the result means depends on which cancer you have and what the rest of the panel shows.

Can I ask for extra markers to be added to my report?

The decision rests with your oncologist and pathologist. Additional markers are ordered when they would answer a specific diagnostic question, not as a routine addition. If you think a marker relevant to your cancer type is missing, ask your oncologist whether it is indicated for your case and why it was not included. A second pathology opinion is also a reasonable option if you remain uncertain after that conversation.

My HER2 result is 2+. Is that positive or negative?

A score of 2+ is borderline — it is not a final positive or negative result. It means a follow-up test, usually FISH or CISH, is needed on the same tissue block to check whether HER2 is truly amplified at the gene level. That second test will give a clear answer. Ask your oncologist when the FISH or CISH test was or will be requested so you know where things stand.

Is IHC the same as genetic testing?

No. IHC detects proteins on the tumour cell surface using antibody staining. Genetic tests, such as FISH or next-generation sequencing, look at DNA inside the cell. Some questions — like HER2 status — need both: IHC first, then FISH to confirm a borderline result. Others, like MSI status, can be assessed by IHC (the MMR panel), molecular testing, or both. Your oncologist will tell you which method is appropriate for your situation.

Why was IHC ordered if I already have a cancer diagnosis?

A cancer diagnosis often happens in stages. The initial result may confirm that cancer cells are present, but IHC tells the pathologist what type of cell they are and where they originated. Two tumours that look similar under a standard microscope can behave very differently once IHC identifies them as distinct subtypes. That distinction determines which treatment path is considered, so the diagnosis is generally not complete without the IHC panel.

Do I need to repeat IHC if I change hospitals?

Usually not, if your original pathology block and report are available. Most centres will request the original tissue block and re-examine it rather than asking for a new biopsy. Carry a copy of your pathology report and ask the new centre whether they need the original block sent to them. If the block is unavailable or the tissue quality is poor, your oncologist and pathologist will decide together whether repeat testing is needed.

Full index

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