IHC is an adjuvant or additive test methodology using an antibody directed against a specific target or marker. IHC is able to bind to specific receptor sites, called epitopes, which provide a method to detect 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 experienced in breast pathology identify suspected breast cancer which may be detected by mammography, palpitation, or other examination by 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 in that the results of receptor studies help to assess prognosis and guide treatment and disease management.