Immunohistochemistry of estrogen receptor protein in paraffin sections: effects of enzymatic pretreatment and cobalt chloride intensification

Monoclonal antibodies provide important tools for the demonstration of estrogen receptors (ERs) in cases of breast cancer. This study reports an improved immunohistochemical method for the demonstration of ER in formalin-fixed paraffin-embedded tissue samples using the Abbott monoclonal antibody to ER protein. Tissue sections were pretreated briefly with trypsin, followed by DNase before the performance of the immunohistochemical reaction and cobalt chloride was used to intensify the color of the diaminobenzidine reaction product. In 20 cases, the results in paraffin sections were compared with biochemical assays with the dextran-coated charcoal technique or with immunohistochemistry performed on frozen sections. There was an excellent correlation between the results obtained with all three methods. The introduction of cobalt chloride into the chromogen solution significantly increased the sensitivity of this approach as compared with the use of diaminobenzidine alone.