Predictive factors of breast cancer evaluated by immunohistochemistry

Hormone receptor and Her2 protein overexpression evaluated by immunohistochemistry (IHC) is widely validated as a predictive factor in breast cancer. The quality of the IHC reaction is influenced by tissue fixation and processing. Over- and underfixation deeply affect IHC results. Antigen retrieval may improve IHC but it does not recover tissue from autolysis or overfixation. The choice of primary antibody for IHC as to its sensitivity and specificity in relation to therapeutic response represents an important stage. Apart from mouse monoclonal antibodies, new rabbit monoclonal antibodies are commercially available, such as clones anti-ER SP1 and B644, anti-PR SP2 and B645 and anti-Her2 SP3 and 4B5. They represent an alternative to hormone receptor and Her2 evaluation by IHC. New polymeric non-biotinylated detection systems are also available and allow accurate and strong marking with no stromal and no non-specific cytoplasmic staining due to endogenous biotin. The most recommended cut off for estrogen and progesterone receptors (ER and PR) is more than 1% of positive cells with moderate or strong staining intensity (Allred's scoring system). New guidelines for Her2 evaluation by IHC show a cut off of more than 30% of positive cells with strong intensity (3+) that correlates better with gene amplification. The 2+ cases are now considered indeterminate and should be confirmed by fluorescence in situ hybridisation (FISH) or chromogenic in situ hybridisation CISH. A quality control of pre-analytical, analytical and post-analytical phases of IHC is recommended in order to optimize results.