PAP immunoperoxidase method demonstrating endogenous estrogen in breast carcinomas.

A PAP immunoperoxidase method for demonstrating estrogen receptors in breast carcinomas is introduced. Whereas other methods pretreat the specimen with exogenous estrogen in high (unphysiologic) doses, this method demonstrates endogenous estrogen without such pretreatment. Experiments showed endogenous estrogen remaining in the formalin-fixed, paraffin-embedded breast tumors in sufficient amounts to be detected by the PAP method. The method can discriminate hormone responsive cells from hormone secreting cells because most responsive cells demonstrate both the cytoplasmic and nuclear stain and most secreting cells only the cytoplasmic stain. The method was applied to 277 human breast carcinomas, of which 197 (71.1%) were positive and 80 (28.9%) negative. These figures were comparable to those obtained by the biochemical methods. This PAP method may serve as an alternative to the biochemical assays of estrogen receptors.