Immunocytochemical staining of progesterone receptor in paraffin sections of human breast cancers.

Monoclonal antibodies (mAB) against progesterone receptor (PR) and the peroxidase-antiperoxidase (PAP) method to visualize PR in paraffin sections from 68 human breast cancers were used. Ten mAB, which recognize human PR on frozen sections, were tested. Six could detect PR in paraffin sections, with Li 417, LET 456, and LET 126 giving the best results. LET 126 antibody was used for most further studies. The effects of fixation with picric acid-formaldehyde (PAF), buffered-formalin, or with Bouin solution were investigated; all fixation methods allowed PR immunolabeling, although PAF or buffered formalin usually gave the best results. Positive staining was seen in the nucleus of carcinoma cells. Variations in intensity and extent of immunoreactivity were observed in all sections and among different regions of the same specimen. These were probably related to the heterogeneity of the tumor cell population. Results were compared with the PR content in the respective tumor tissues, determined by steroid-binding assay, and with immunocytochemistry on frozen sections. It was shown that there were correlations between the immunocytochemical staining (positive or negative) and the steroid binding assay (80%) and between the immunocytochemical staining on paraffin sections and on frozen sections (78%). Weaker intensity and fewer number of PR-positive cells were found for paraffin-embedded tumors. Estrogen receptors were also detected on adjacent sections from the same paraffin-embedded tissues by use of monoclonal anti-ER antibodies (ERICA-kit[Abbott Laboratories, Chicago, IL]) and DNase pretreatment. In conclusion, this immunocytochemical method for detection of PR and ER on paraffin sections offers an alternative to frozen tissue. It allows histologic and immunocytochemical studies on the same sample and retrospective studies on stored tissue blocks.