ESTROGEN-RECEPTOR IMMUNOCYTOCHEMISTRY IN PARAFFIN-EMBEDDED TISSUES WITH ER1D5 PREDICTS BREAST-CANCER ENDOCRINE RESPONSE MORE ACCURATELY THAN H222SP-GAMMA IN FROZEN-SECTIONS OR CYTOSOL-BASED LIGAND-BINDING ASSAYS

BACKGROUND. Historically, estrogen receptor (ER) determinations have b een made by the ligand-binding assay of tumor homogenates, primarily b y the dextran-coated charcoal method (DCC). Immunocytochemical assays (ICA) for ER are more recent and have been executed mostly on frozen s ections with the monoclonal antibody H222Sp gamma (H222). Lately, new monoclonal antibodies derived by recombinant ER technology have been d eveloped that work well on paraffin embedded, formalin fixed tissue se ctions. However, there is little information as to whether such assays prognosticate endocrine response. METHODS. Using antigen retrieval, t he immunoglobulin G(I) monoclonal antibody ER1D5, and the streptavidin -biotin detection system, 74 patients with breast cancer in whom endoc rine 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 pa raffin provided the highest correlation with endocrine response (Kenda ll'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 sig nificantly with DCC (Kappa Statistic [K] = 0.204; P < 0.02). H222 in f rozen sections also correlated moderately with endocrine response (r = 0.34; P < 0.001). CONCLUSIONS. ER can be detected in routine tissue s ections 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. (C) 1996 American Cance r Society.