Background: Estrogen receptor alpha (ER) expression is the best prognostic and predictive factor of hormone dependency of human breast cancers. Unlike enzyme immunoassay (EIA), which has been widely used to evaluate ER status in breast cancer, immunohistochemical assay (IHC) can detect ER in a small amounts of tissue with detailed localization. Although there is a sufficient number of ER antibodies against various regions of the protein, the reliability of IHC staining is only well understood for a few. IHC and EIA for the evaluation of the ER status of human breast cancer, therefore, should be compared using the same breast cancer tissues.
Methods: Five different ER antibodies (1D-5, C-314, G-20, C-311 and HC-20) that identify different amino acid sequences were used. The evaluation of ER status by IHC using these antibodies was compared with EIA concomitantly in 97 primary human breast cancer tissues
Results: The positivity rate for EIA was 68%. That of IHC for antibodies 1D-5, C-314, G-20, C-311 and HC-20 was 50.5%, 47.4%, 46.4%, 44.3% and 57.7%, respectively. The concordance between EIA was 76.3% for 1D-5 and 77.3% for HC-20, which is statistically highly significant (p<0.0001); Other antibodies were not.
Conclusions: HC-20 is most suitable in the evaluation of the ER status of human breast cancers using the IHC method. Although antibody 1D-5 is also available, C-314, G20 and C-311 are unreliable in such an evaluation.