General pathology · The pathology laboratory
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
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 | Epithelial cells | Confirm that a tumour is a carcinoma |
| CK7 and CK20 | Organ-dependent keratin patterns | CK7+/CK20− in lung and breast; CK7−/CK20+ in colon |
| CD45 (leucocyte common antigen) | Leucocytes | Separate lymphoma from carcinoma |
| CD20 and CD3 | B cells and T cells | Classify a lymphoma |
| CD15 and CD30 | Reed–Sternberg cells | Classic Hodgkin lymphoma |
| S-100, SOX10, HMB-45, Melan-A | Melanocytic cells (S-100 also in nerves) | Melanoma |
| TTF-1 | Lung and thyroid epithelium | Lung adenocarcinoma, thyroid carcinoma |
| CDX2 | Intestinal epithelium | Metastasis of colorectal origin |
| PSA and NKX3.1 | Prostatic epithelium | Metastasis of prostatic origin |
| ER, PR and HER2 | Hormone receptors and HER2 | Breast cancer: prognosis and treatment |
| CD117 (KIT) and DOG1 | Interstitial cells of Cajal | Gastrointestinal stromal tumour |
| Chromogranin and synaptophysin | Neuroendocrine cells | Neuroendocrine tumours |
| Calretinin and WT1 | Mesothelium | Mesothelioma versus adenocarcinoma |
| CD99 | Membrane of small round cells | Ewing sarcoma |
| MLH1, PMS2, MSH2, MSH6 | 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.
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.
Related
- Special stains in diagnosis: Congo red, Prussian blue, PAS, Ziehl–Neelsen, Gram
- Molecular pathology: PCR, FISH, sequencing and liquid biopsy
- Differentiation and anaplasia: how a tumour cell looks under the microscope
- Tumour markers: serum and tissue, and what each one is for
- From specimen to report: fixation, margins and the pathology report
- Naming tumours: -oma, carcinoma, sarcoma, and the misleading names
Related conditions
- Carcinoma of unknown primary
- Breast cancer
- Non-Hodgkin lymphoma
- Hodgkin lymphoma
- Melanoma
- Lung cancer
- Colorectal cancer
- Prostate cancer
- Gastrointestinal stromal tumour (GIST)
- Pancreatic neuroendocrine tumours (VIPoma, glucagonoma, somatostatinoma, non-functioning)
- Malignant pleural mesothelioma
- Ewing sarcoma
- Lynch syndrome (hereditary non-polyposis colorectal cancer)
- Cervical intraepithelial neoplasia (cervical dysplasia)
Elsewhere in DurgiPedia
- Microscopy and stains: H&E, PAS, trichrome, silver, immunohistochemistry
- Monoclonal antibodies and biologics: naming and targets
- Antibody structure and isotypes (IgG, IgA, IgM, IgE, IgD)
- Tumour markers: principles of use
In Pharmacology
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 (National Cancer Institute, 2025); Testing for HER2 in Breast Cancer: A Continuing Evolution (Pathology Research International (PMC), 2011); Pathology Reports (National Cancer Institute, 2023).
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Representative model, for educational purposes only.