COMPARISON OF 2 ANTIBODIES FOR EVALUATION OF ESTROGEN-RECEPTORS IN PARAFFIN-EMBEDDED TUMORS

Estrogen receptor (ER) content in breast cancer specimens is correlate d with a prolonged disease free survival and increased likelihood of r esponse to hormone therapy. Relatively few anti-ER antibodies are curr ently available for use in formalin-fixed, paraffin-embedded tissue. R ecently, a new anti-ER monoclonal antibody (ERID5; AMAC, Westbrook, Ma ine) was generated which requires antigen retrieval by microwave oven heating for detection in routinely processed tissue. The specific aim of this study was to compare the ERID5 antibody with the commercially available rat monoclonal (ER-ICA; Abbott, Chicago, IL) which requires proteolytic enzyme digestion for detection in paraffin-embedded tissue . Sections from 20 cases of primary breast carcinoma previously assaye d by dextran-coated charcoal (DCC) analysis were examined. Quantitatio n of ER antibody staining was performed without knowledge of the DCC v alues. Specimens containing greater than or equal to 20% specifically stained malignant cells were considered ER positive. The sensitivity a nd specificity of visual ER-ICA immunostaining were 57% and 83%, respe ctively. The sensitivity and specificity of visual ERID5 immunostainin g were 93% and 50%, respectively. The predictive value of positive sta ining was 89% for the ER-ICA antibody and 81% for the ERID5 antibody. The predictive value of negative staining was 45% for the ERICA antibo dy and 75% for the ERID5 antibody. Previous studies have demonstrated a linear correlation between DCC values and the positive nuclear area (PNA) generated by image analysis for ER-ICA immunostaining. In the pr esent study, a similar correlation between DCC value and ERID5 percent age PNA was observed (R = 0.670; P < 0.001). This study suggests that both ER-ICA and ERID5 antibodies are adequate to depict the performanc e of ER in routinely processed tissue, although ERID5 staining may be more sensitive.