Use of Immunohistochemistry (IHC) for Breast Tumor Classification

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Use of Immunohistochemistry (IHC) for Breast Tumor Classification

IHC is an adjuvant or additive test methodology that uses an antibody directed against a target antigen (marker). IHC techniques are used to bind the antibody to specific receptor sites, called epitopes located on the target antigen. This method makes it possible to determine the presence or absence of certain factors that define a patient's breast cancer, most frequently represented in IHC as a measure of protein expression.
Pathologists identify suspected breast cancer through microscopic review of hematoxylin and eosin (H&E) stained slides. Additive tests, such as IHC, are used to further assist the pathologist in tumor typing and to 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 to classify the specific type of tumor a patient may have. For example, E-cadherin testing is useful to classify the tumor as ductal or lobular. Cytokeration 7, cytokeratin 5/6, or cytokeratin 14 can be used to distinguish an epithelial from a myoepithelial type. Receptor studies such as ER, PR, and HER2 further identify the specific type and characteristics of a patient's tumor and are unique and predictive, in that the results of receptor studies are strongly correlated with prognosis and guide the selection of specific treatments.