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Background: Historically, estrogen receptor (ER) determinations have been made by the ligand-binding assay of tumor homogenates, primarily by the dextran-coated charcoal method (DCC). Immunocytochemical assays (ICA) for ER are more recent and have been executed mostly on frozen sections with the monoclonal antibody H222Sp gamma (H222). Lately, new monoclonal antibodies derived by recombinant ER technology have been developed that work well on paraffin embedded, formalin fixed tissue sections. However, there is little information as to whether such assays prognosticate endocrine response., Methods: Using antigen retrieval, the immunoglobulin G1 monoclonal antibody ER1D5, and the streptavidin-biotin detection system, 74 patients with breast cancer in whom endocrine response was known were assayed and the results compared with ER by DCC and ER by ICA in frozen section with H222., Results: ER1D5 in paraffin provided the highest correlation with endocrine response (Kendall's tau [r] = 0.57; P<0.001) whereas ER by DCC failed to correlate (r= -0.002; P<0.99). ER1D5 in paraffin correlated weakly though significantly with DCC (Kappa Statistic [K] = 0.204; P<0.02). H222 in frozen sections also correlated moderately with endocrine response (r = 0.34; P<0.001)., Conclusions: ER can be detected in routine tissue sections processed with antigen retrieval and ER1D5, and can be relied upon to provide accurate prognostic information regarding response to endocrine therapies in breast cancer patients.

Estrogen receptor immunocytochemistry (ERICA) is favored over dextran-coated charcoal (DCC) or sucrose gradient assay (SGA) by many pathologists and oncologists since it allows an estimation of tumor cell and tissue heterogeneity and permits assays to be performed on specimens not suitable for DCC/SGA. Additionally, ERICA can be performed with greater ease and with less expense at the level of the community hospital pathology laboratory. Initially, like DCC/SGA, ERICA had to be done on fresh or frozen tumor samples or face a significant loss in sensitivity when applied to formalin-fixed, paraffin-embedded sections. Recently, several anti-estrogen receptor (ER) antibodies have appeared which can be successfully employed to assay routinely prepared tissue sections if used in conjunction with new antigen-retrieval techniques such as the microwave oven and citrate buffers. However, more work is needed to correlate results of these new procedures with biochemical ER assays, endocrine response, and survival before they can be reliably employed as prognostic parameters. Furthermore, if any ER assay is to be useful and valid, strict attention must be paid to details of specimen collection, freezing, and fixation in order to inhibit receptor degradation and false negative results.