Author: Brian Wu PhD. MD Candidate, Keck School of Medicine; Chief Editor: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, July 2015.
Immunohistochemistry (IHC) is considered to be an advanced form of histopathology. It is not usually used initially, but rather added when routine/regular histological testing cannot provide the answers which clinicians need to form a diagnosis – and thus a plan of care.
IHC uses primary antibodies to label a protein, then follows this up with a secondary antibody which is bound to the primary one. In immunoperoxidase staining, an antibody is joined to a enzyme, peroxidase, that catalyses a reaction in which the protein is specifically stained brown. IHC can also involve fluorescently labelled antibody, so that when viewed under a light microscope, a certain pattern will be observed from the emitted fluorescence.
The IHC pattern is considered diagnostic. This is why IHC is often used in situations where a presence or absence of certain proteins can form a basis for a diagnosis. It can also be used to distinguish between two different disease processes that may otherwise appear similar to the pathologist.
The most common process of preparing immunohistochemical slides is as follows:
A wide variety of immunohistochemical stains is used to identify different tumours and other neoplasms. Some of the most common are listed in the table below.
|Alpha-fetoprotein||Used to detect hepatocellular carcinomas and germ cell neoplasms|
|Alpha-1-antichymotrypsin||Can identify soft tissue histiocytomas and fibroxanthomas of the skin|
|BCL2||Used to distinguish between basal cell carcinomas and trichoepitheliomas
Image is of primary cutaneous diffuse large B cell lymphoma
|Calponin||Can differentiate between benign and malignant breast lesions|
|CD30||Can be used in the diagnosis of Hodgkin lymphoma and anaplastic lymphomas
Image is of lymphomatoid papulosis
|CD31||Helps to identify endothelial tumors
Image is of epithelioid angiosarcoma
|CD34||Distinguishes different endothelial tumours
Image is of the cellular variant of dermatofibroma
|CD56||Used in the diagnosis of non-Hodgkin lymphomas, leukemias and small cell carcinomas|
|Chromogranin||Can mark some endocrine tumours|
|EMA||Used to identify eccrine neoplasms, Paget disease and sebaceous carcinomas
Image is of clear cell acanthoma
|Factor 8||Used to mark megakaryocytes and endothelial cells|
|Factor 13||Can help clinicians distinguish between dermatofibrosarcomas and dermatofibromas
Image is of dermatofibroma
|HMB 45||Used to detect melanocytes, naevus cells and melanomas
Image shows staining in melanoma and not in adjacent naevus
|Cytokeratin High Molecular Weight||Used to detect ductal carcinomas, squamous cell carcinomas and other epithelial neoplasms
Image is of Pagetoid infiltration of the epidermis by breast cancer
|Cytokeratin 20||Can help identify adenocarcinomas of the gastrointestinal and reproductive system as well as gastrointestinal epithelial tumors
Image is of Merkel cell carcinoma
|MART, Melan-a||Can help identify melanocytic naevus cells and melanomas|
|S-100||Used to mark tumours of the melanocytes, both naevi and melanomas
Image is of folliculotropic metastatic melanoma
|Vimentin||Helps identify mesenchymal tumors|
The advantages of IHC include:
The disadvantages of IHC are as follows:
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