Immunohistochemical evaluation of estrogen and progesterone receptors in paraffin-embedded, formalin-fixed endometrial tissues: comparison with enzyme immunoassay and immunohistochemical analysis of frozen tissue.

Monoclonal antibody (MoAb) 1D5 with specificity to the estrogen receptor (ER), MoAb 1A6, and a polyclonal antibody (PoAb) (the latter two with specificity to the progesterone receptor [PgR]) were used to stain microwave-pretreated sections of formalin-fixed, paraffin-embedded normal and malignant endometrial tissues (n = 60). The tissues were previously evaluated for ER and PgR by enzyme immunoassay (EIA) (n = 44) and immunohistochemical analysis of frozen tissue (ICAfroz, n = 59). With results of EIA as a reference, the ER-1D5 method yielded a better agreement on receptor status, i.e., positive versus negative (74 vs. 51%) and a higher sensitivity (71 vs. 45%) but a similar high specificity (100%) than the ER-ICA method. Compared with results of PgR-EIA, the immunohistochemical assays for PgR gave similar results as to agreement (86-95%) and sensitivity (95-97%). Quantitative agreement on the fraction of cells stained for ER and PgR by immunohistochemical analysis in frozen and formalin-fixed tissue was obtained in approximately 60% of the cases. The results of semiquantitation were correlated with the results of both ICA and EIA. The MoAbs 1D5 and 1A6, as well as the anti-PgR PoAb, thus seem to be valid for evaluation of ER and PgR status in formalin-fixed endometrial tissue. Differences in the specificity of the Abs and in the sensitivity of the methods used to demonstrate ER and PgR might explain some of the discordant findings.