Detection of estrogen receptor in breast and endometrial carcinoma by the immunoperoxidase technique

Paraffin‐embedded tissues from 15 women with breast or endometrial carcinomas were analyzed in a study designed to explore the possible value and validity of an immunoperoxidase method for the detection of estrogen receptor in formalin‐fixed paraffin‐embedded tissue. Results were compared with biochemical assays for estrogen receptor performed on cytosols of fresh tissue from the same patients. There was complete correlation in nine of 15 (60%) of the tumors analyzed. Four cases (26.7%) were judged positive for estrogen binding sites by immunoperoxidase but were negative for estrogen receptor by biochemical assays; in two cases the converse was observed. The immunohistologic technique is relatively rapid and utilizes fixed paraffin sections of the same tissue that is used for standard histologic diagnosis. The provision of a permanent record that can be kept for future reference provides an advantage over immunofluorescence methods that have been advanced for the detection of estrogen receptors. The excellent morphology achieved permits an assessment of the staining of individual cells in relation to the usual histologic criteria employed in the diagnosis of breast and endometrial cancer. This stands in contrast to biochemical cytosol‐based assays that take no account of variations in receptor expression by the tumor cells or variations in the proportion of the assayed material that is in fact neoplastic as distinct from supporting stroma and connective tissue.