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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. Immunohistochemistry is not usually used initially but is added when routine/regular histological testing is insufficient to form a diagnosis.
IHC uses primary antibodies to label a protein, then uses a secondary antibody which is bound to the primary one. In immunoperoxidase staining, an antibody is joined to an 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, demonstrating nuclear, membranous or cytoplasmic patterns. 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:
The advantages of IHC include:
The disadvantages of IHC are as follows:
Hundreds of immunohistochemical stains are used to identify different tumours and other neoplasms. Just a few of the IHC stains used in dermatology are listed below.
|IHC Stain||Uses/Image caption|
|BCL2||Used to distinguish between basal cell carcinomas and trichoepitheliomas|
|CD3||T-cell marker; strongly positive in mycosis fungoides|
|CD4||Helper T-cell marker|
|CD8||Suppressor T-cell marker|
|CD30||Can be used in the diagnosis of Hodgkin lymphoma and anaplastic lymphomas. Large cells: Golgi apparatus and membranous staining|
|CD31||Helps to identify endothelial tumour|
|CD34||Distinguishes different endothelial tumours and is positive in dermatofibrosarcoma|
|CD56||Used in the diagnosis of non-Hodgkin lymphomas, leukaemias and small cell carcinomas|
|CD117||Marker for KIT receptor and positive in various tumours including mastocytosis|
|CDKN2A (p16)||Tumour suppressor marker positive in HPV-associated tumours, actinic keratoses and squamous cell carcinoma|
|CK (various)||Cytokeratins can be used to help distinguish benign from malignant adnexal tumours|
|CK 20||Specific for Merkel cell carcinoma. Can help identify adenocarcinomas of the gastrointestinal and reproductive system as well as gastrointestinal epithelial tumours|
|Cytokeratin High Molecular Weight||Used to detect ductal carcinomas, squamous cell carcinomas and other epithelial neoplasms|
|EMA||Used to identify eccrine neoplasms, Paget disease and sebaceous carcinomas|
|Factor 13||Can help clinicians distinguish between dermatofibrosarcoma and dermatofibroma|
|HHV8||Human herpesvirus 8|
|HMB 45||Used to detect melanocytes, especially in melanoma but negative in desmoplastic melanoma|
|Melan-a||Can help identify melanocytic naevus cells and melanomas|
|PDL1||Programmed death-ligand 1|
|S-100||Used to mark tumours of the melanocytes, both naevi and melanoma|
|SMA||Smooth muscle antigen|
|SOX-10||Nuclear marker for melanocytic tumours|
|Treponema pallidum||Demonstrates organisms in secondary syphilis|
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