Determination of estrogen receptor in primary breast cancer using two different monoclonal antibodies, and correlation with its mRNA expression

Estrogen receptor (ER) protein status was investigated in the MCF-7 cell li ne and 70 invasive ductal carcinomas of the breast, This was achieved by im munohistochemical assay (IHA) using two different monoclonal antibodies (ER -1D5 and AER311), which are able to recognize either the amino or carboxyl terminal. The staining results were assessed in terms of index score, and c ompared with the ER alpha mRNA expression, which was determined by reverse transcription-polymerase chain reaction for the positions of exons 5 and 7, MCF-7 showed similar immunoreactions with both antibodies, and expressed t he wild-type (WT) ER mRNA coexpressing deletions of exons 5 and 7, Although there was a significant difference between the ER-1D5 and AER311 indices i n the tissue samples (20.5 +/- 27.2 and 5.7 +/- 16.4; P < 0.001), in the ma jority of cases ER mRNA expression patterns were similar to that of MCF-7, and WT ER mRNA was expressed in all cases that yielded PCR products. It was concluded that a number of palpable breast cancers lack the carboxyl termi nal of the ER protein, regardless of WT ER mRNA expression. These results s uggest that the incidence of WT ER mRNA in such cancers is lower than that in the MCF-7 cell line, or that WT ER is less stable.