Immunohistochemistry (IHC) is an adjuvant or additive test methodology that uses an antibody directed against a target antigen (marker). IHC techniques bind the antibody to specific receptor sites and epitopes on the target antigen. This method makes it possible to determine the presence or absence of particular factors that define a patient's breast cancer. This is most frequently represented in IHC as a measure of protein expression.
Pathologists identify suspected breast cancer through a microscopic review of hematoxylin and eosin (H&E) stained slides. Additive tests, such as IHC, further assist the pathologist in tumor typing and confirm or rule out a suspected diagnosis.
Information determined by histological testing and microscopic examination includes:
- Identification of focal areas or extent of invasion
- Status of the surgical margins
- Lymph node metastases
- Determination and classification of tumor type ( lobular versus ductal, luminal versus basal or myoepithelial)
While not predictive of specific therapy, several other antibodies used in IHC techniques help classify a patient's tumor type. For example, E-cadherin testing is helpful to classify the cancer as ductal or lobular. Cytokeratin 7, cytokeratin 5/6, or cytokeratin 14 can distinguish an epithelial from a myoepithelial type. Receptor studies such as ER, PR, and HER2 further identify a patient's tumor's specific types and characteristics. They are unique and predictive in that the results of receptor studies strongly correlate with prognosis and guide the selection of particular treatments.
