Abstract
Surgical biopsy specimens of 179 breast carcinoma were studied by steroid-binding and immunohistochemical assays or oestrogen and progesterone receptors (ER, PR) in order to explore reasons for discordant results between the two assay types. Receptor statuses in 18% of ER assays and 30% of PR assays were in disagreement. Immunohistochemistry-positive steroid-binding-negative status predominated among the discordant ER assays, while the discordant PR assays displayed the opposite situation. In discordant assays receptor concentration was significantly more often close to the cut-off (10-50 fmol mg-1) than in the concordant ones. Low binding affinity (high Kd) was also significantly associated with disagreeing assay results. These observations clearly indicate that immunohistochemical ER and PR assays measure high-affinity binding components (i.e. type I receptors) in steroid-binding assays. ER but not PR assays in premenopausal women disagreed more often than those in post-menopausal women. Such factors as histological type, specimen size in steroid-binding assay, grade of malignancy and tumour necrosis were statistically unrelated to agreement or disagreement of receptor assays.
Highlights
This study focuses on possible reasons for discordant results between steroid binding and immunohistochemical assays in 179 consecutive surgical biopsy specimens of female breast carcinoma
Our results indicate that the immunohistochemical ER and PR assays recognise the high affinity steroid binding component ('type I receptor')
Low epithelial cell content within the tumours was, significantly correlated with discordance confirming that specimens with small amounts of carcinoma cells are a problem encountered in DCC assays
Summary
Tumour specimens were processed to paraffin sections and stained using standard histological procedures. In the negative control staining, normal rat immunoglobulin replaced the monoclonal anti-ER. The detailed immunoperoxidase staining procedure has been described earlier (Helin et al, 1988a, 1989). Frozen sections of rabbit uterus were used as positive controls, and negative control staining was done using non-immune mouse immunoglobulin instead of the specific antibody. The concentrations of ER and PR in tumour extract cytosols were determined by a radioligand binding assay using multipoint titration with seven different concentrations of tritiated estradiol or Org 2058 as ligands. Assays with Kdk0.2 nM (ER) or ) 0.3 nM (PR) were scored negative except for the data, where the cut-off in receptor concentration was the only criterion for positivity Assays with Kdk0.2 nM (ER) or ) 0.3 nM (PR) were scored negative except for the data in Figure 3, where the cut-off in receptor concentration was the only criterion for positivity
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