Immunohistochemistry (IHC) is the most commonly used method for measuring and detecting ER and PR status in breast tumors. In the 1970s, the "positive” and “negative” cut-off points for ER and PR were established by ligand binding assays (LBAs). By the mid-1990s, LBAs were replaced by IHC, as breast cancer studies began to consistently show IHC to be equivalent to or superior to LBAs in predicting response to hormone therapy (with levels as low as 1% of positive staining cells).
IHC is a relatively rapid and cost-effective testing method. Unlike the older LBA biochemical assays, IHC can be carried out on small tumors, including breast needle core biopsies.
Some drawbacks to IHC methods include an element of subjectivity in scoring (it is a qualitative test method) and variability in results, especially in comparisons between laboratories, due to variations in fixation and tissue processing.
Table 2. Common IHC Staining Patterns Manual Observation.| Localization | Observed Staining Pattern | Evaluation - Scoring |
| Nuclear only | Dense staining is limited to the nucleus | Positive-negative % positive intensity |
| Cytoplasmic only | Staining limited to cytoplasm | Positive-negative % positive intensity |
| Membrane only | Staining limited to membrane | Positive-negative % positive intensity |
Combinations (nuclear,
cytoplasmic, membranous) | Assay may determine the location
or staining pattern | Positive-negative % positive intensity |
2. Clinical and Laboratory Standards Institute. Quality Assurance for Design Control and Implementation of Immunohistochemistry Assays. 2nd ed.CLSI document I/LA28-A2. Wayne, PA: CLSI; 2011.
