[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [The pathology laboratory](https://durgical.com/en/general-pathology/#a-lab) › Immunohistochemistry: the principle and the markers to know

[General pathology](https://durgical.com/en/general-pathology/) · [The pathology laboratory](https://durgical.com/en/general-pathology/#a-lab)

# Immunohistochemistry: the principle and the markers to know

- Technique

An antibody that recognises a protein binds to it in the section, and a colour reaction shows which cells carry it.

Updated 2026-11-01

## Key points

- A panel, not a single marker: no marker is fully specific.
- CK7+/CK20− lung and breast; CK7−/CK20+ colon.
- CD15 and CD30 = Reed–Sternberg (classic Hodgkin); CD117 = GIST.
- S-100 and SOX10 = melanoma; TTF-1 = lung and thyroid; CDX2 = intestine.
- HER2: 0–1+ negative, 2+ equivocal (do in situ hybridisation), 3+ positive.
- Location matters: ER is nuclear, HER2 is membranous.

## What it is

Immunohistochemistry uses labelled antibodies to locate proteins in a tissue section. It tells the lineage of a tumour (epithelial, lymphoid, melanocytic, mesenchymal), suggests its origin when the primary is unknown and measures treatment targets such as hormone receptors and HER2. It is always read as a panel and together with the H&E morphology.

## Step by step

- Formalin-fixed tissue loses part of its protein shape; heat-induced antigen retrieval restores it.
- A primary antibody binds the target protein (the antigen) in the section.
- An enzyme-linked detection system binds the primary antibody.
- The enzyme turns a chromogen into a coloured precipitate, usually brown.
- The pathologist assesses which cells stain, how many, how strongly and where: nucleus, cytoplasm or membrane.
- Positive and negative controls from the same run confirm that the technique worked.

## Immunohistochemistry markers: what they flag

| Marker | What it flags | Typical use |
| --- | --- | --- |
| [Cytokeratins](https://durgical.com/en/conditions/carcinoma-of-unknown-primary/) | Epithelial cells | Confirm that a tumour is a carcinoma |
| [CK7 and CK20](https://durgical.com/en/conditions/colorectal-cancer/) | Organ-dependent keratin patterns | CK7+/CK20− in lung and breast; CK7−/CK20+ in colon |
| [CD45 (leucocyte common antigen)](https://durgical.com/en/conditions/non-hodgkin-lymphoma/) | Leucocytes | Separate lymphoma from carcinoma |
| [CD20 and CD3](https://durgical.com/en/conditions/non-hodgkin-lymphoma/) | B cells and T cells | Classify a lymphoma |
| [CD15 and CD30](https://durgical.com/en/conditions/hodgkin-lymphoma/) | Reed–Sternberg cells | Classic Hodgkin lymphoma |
| [S-100, SOX10, HMB-45, Melan-A](https://durgical.com/en/conditions/melanoma/) | Melanocytic cells (S-100 also in nerves) | Melanoma |
| [TTF-1](https://durgical.com/en/conditions/lung-cancer/) | Lung and thyroid epithelium | Lung adenocarcinoma, thyroid carcinoma |
| [CDX2](https://durgical.com/en/conditions/colorectal-cancer/) | Intestinal epithelium | Metastasis of colorectal origin |
| [PSA and NKX3.1](https://durgical.com/en/conditions/prostate-cancer/) | Prostatic epithelium | Metastasis of prostatic origin |
| [ER, PR and HER2](https://durgical.com/en/conditions/breast-cancer/) | Hormone receptors and HER2 | Breast cancer: prognosis and treatment |
| [CD117 (KIT) and DOG1](https://durgical.com/en/conditions/gastrointestinal-stromal-tumour/) | Interstitial cells of Cajal | Gastrointestinal stromal tumour |
| [Chromogranin and synaptophysin](https://durgical.com/en/conditions/pancreatic-neuroendocrine-tumours/) | Neuroendocrine cells | Neuroendocrine tumours |
| [Calretinin and WT1](https://durgical.com/en/conditions/malignant-pleural-mesothelioma/) | Mesothelium | Mesothelioma versus adenocarcinoma |
| [CD99](https://durgical.com/en/conditions/ewing-sarcoma/) | Membrane of small round cells | Ewing sarcoma |
| [MLH1, PMS2, MSH2, MSH6](https://durgical.com/en/conditions/lynch-syndrome/) | Mismatch repair proteins | Screening for Lynch syndrome |

## Markers

- Cytokeratins
- Vimentin
- Desmin
- CD45
- CD20
- CD3
- CD30
- S-100
- SOX10
- TTF-1
- CDX2
- ER
- PR
- HER2
- Ki-67
- p16
- PD-L1

## Clinical notes

- Metastasis of unknown primary: a panel (cytokeratins, CK7/CK20, TTF-1, CDX2, PAX8, ER) points to the organ of origin.
- Breast cancer: ER- and PR-positive tumours are candidates for endocrine therapy; HER2 3+ means HER2-positive; 2+ is equivocal and is settled by in situ hybridisation.
- Ki-67 marks cells that are in the cell cycle: it estimates how fast a tumour proliferates.
- Diffuse, strong p16 in cervical and oropharyngeal lesions suggests high-risk HPV involvement.
- Loss of a mismatch repair protein (for example MLH1 with PMS2) in a colorectal cancer leads to testing for Lynch syndrome.

## Memory aid

Seven up top, twenty down below: CK7 in the upper organs (lung, breast), CK20 in the colon further down.

## Test yourself

Think of the answer, then tap the question to see it.

## Which cytokeratin pattern suggests a colorectal origin for a metastasis?

CK7-negative and CK20-positive, often with CDX2 positivity.

## Which markers characterise the Reed–Sternberg cells of classic Hodgkin lymphoma?

CD15 and CD30 positive; they are usually CD45-negative.

## What is done when a breast cancer is HER2 2+ by immunohistochemistry?

It is considered equivocal and in situ hybridisation is done to see whether the HER2 gene is amplified.

## What is antigen retrieval for?

To restore to formalin-fixed proteins the shape the antibody recognises, so the stain works.

## Which immunohistochemistry marker is typical of gastrointestinal stromal tumour?

CD117 (KIT), often together with DOG1.

[Add to my cards (5)](https://durgical.app/estudiar/?add=/en/general-pathology/immunohistochemistry-the-principle-and-the-markers-to-know/)

## Related

- [Special stains in diagnosis: Congo red, Prussian blue, PAS, Ziehl–Neelsen, Gram](https://durgical.com/en/general-pathology/special-stains-in-diagnosis-congo-red-prussian-blue-pas-ziehl-neelsen-gram/)
- [Molecular pathology: PCR, FISH, sequencing and liquid biopsy](https://durgical.com/en/general-pathology/molecular-pathology-pcr-fish-sequencing-and-liquid-biopsy/)
- [Differentiation and anaplasia: how a tumour cell looks under the microscope](https://durgical.com/en/general-pathology/differentiation-and-anaplasia-how-a-tumour-cell-looks-under-the-microscope/)
- [Tumour markers: serum and tissue, and what each one is for](https://durgical.com/en/general-pathology/tumour-markers-serum-and-tissue-and-what-each-one-is-for/)
- [From specimen to report: fixation, margins and the pathology report](https://durgical.com/en/general-pathology/from-specimen-to-report-fixation-margins-and-the-pathology-report/)
- [Naming tumours: -oma, carcinoma, sarcoma, and the misleading names](https://durgical.com/en/general-pathology/naming-tumours-oma-carcinoma-sarcoma-and-the-misleading-names/)

## Related conditions

- [Carcinoma of unknown primary](https://durgical.com/en/conditions/carcinoma-of-unknown-primary/)
- [Breast cancer](https://durgical.com/en/conditions/breast-cancer/)
- [Non-Hodgkin lymphoma](https://durgical.com/en/conditions/non-hodgkin-lymphoma/)
- [Hodgkin lymphoma](https://durgical.com/en/conditions/hodgkin-lymphoma/)
- [Melanoma](https://durgical.com/en/conditions/melanoma/)
- [Lung cancer](https://durgical.com/en/conditions/lung-cancer/)
- [Colorectal cancer](https://durgical.com/en/conditions/colorectal-cancer/)
- [Prostate cancer](https://durgical.com/en/conditions/prostate-cancer/)
- [Gastrointestinal stromal tumour (GIST)](https://durgical.com/en/conditions/gastrointestinal-stromal-tumour/)
- [Pancreatic neuroendocrine tumours (VIPoma, glucagonoma, somatostatinoma, non-functioning)](https://durgical.com/en/conditions/pancreatic-neuroendocrine-tumours/)
- [Malignant pleural mesothelioma](https://durgical.com/en/conditions/malignant-pleural-mesothelioma/)
- [Ewing sarcoma](https://durgical.com/en/conditions/ewing-sarcoma/)
- [Lynch syndrome (hereditary non-polyposis colorectal cancer)](https://durgical.com/en/conditions/lynch-syndrome/)
- [Cervical intraepithelial neoplasia (cervical dysplasia)](https://durgical.com/en/conditions/cervical-intraepithelial-neoplasia/)

## Elsewhere in DurgiPedia

- [Microscopy and stains: H&E, PAS, trichrome, silver, immunohistochemistry](https://durgical.com/en/histology/microscopy-and-stains-h-y-e-pas-trichrome-silver-immunohistochemistry/)
- [Monoclonal antibodies and biologics: naming and targets](https://durgical.com/en/immunology/monoclonal-antibodies-and-biologics-naming-and-targets/)
- [Antibody structure and isotypes (IgG, IgA, IgM, IgE, IgD)](https://durgical.com/en/immunology/antibody-structure-and-isotypes/)
- [Tumour markers: principles of use](https://durgical.com/en/biochemistry/topics/tumour-markers-principles-of-use/)

## In Pharmacology

- [Tamoxifen](https://durgical.com/en/pharmacology/tamoxifen/)
- [Letrozole](https://durgical.com/en/pharmacology/letrozole/)
- [Anastrozole](https://durgical.com/en/pharmacology/anastrozole/)

[← All of general pathology](https://durgical.com/en/general-pathology/)

Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Breast Cancer Treatment (PDQ®)–Health Professional Version](https://www.cancer.gov/types/breast/hp/breast-treatment-pdq) (National Cancer Institute, 2025); [Testing for HER2 in Breast Cancer: A Continuing Evolution](https://pmc.ncbi.nlm.nih.gov/articles/PMC3005907/) (Pathology Research International (PMC), 2011); [Pathology Reports](https://www.cancer.gov/about-cancer/diagnosis-staging/diagnosis/pathology-reports-fact-sheet) (National Cancer Institute, 2023).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/immunohistochemistry-the-principle-and-the-markers-to-know/