Quantification of oestrogen receptors in breast cancer: radiochemical assay on cytosols and cryostat sections compared with semiquantitative immunocytochemical analysis.

A radiochemical oestrogen receptor assay on cytosol was correlated with a radiochemical and an immunohistochemical oestrogen receptor assay using cryostat sections from 50 breast cancer specimens. Oestrogen receptors were reliably quantitated in 6 micron cryostat sections with Scatchard analysis using radiolabelled oestradiol, and a good quantitative and qualitative relation with cytosol oestrogen receptor assay was found. Parallel sections were used for routine histological tissue verification and for direct comparison with immunohistochemistry for oestrogen receptor. Specific immunoperoxidase staining with a rat monoclonal antibody was scored by semiquantitative evaluation of the staining intensity of cancer cell nuclei. Oestrogen receptor scoring was highly reproducible when performed by the same observer. The semiquantitative immunohistochemical oestrogen receptor score correlated significantly better with the radiochemical assay on sections than with cytosol assay. Oestrogen receptor in breast cancer can be reliably assayed by semiquantitative evaluation of cryostat sections immunostained for oestrogen receptor, but only if the procedure is adequately standardised. The results underline the importance of cellular heterogeneity as a cause of variation in oestrogen receptor assay evaluation in breast cancer.

Progesterone receptor quantification with radiolabeled promegestone (R 5020) in frozen sections of endometrium and breast cancer tissue.

A technique for the determination of the progesterone receptor content at sections was developed. Series of coverglass-mounted unfixed frozen sections were incubated with [3H]R5020 only, to determine total binding, or with excess unlabeled R5020, to determine non-specific binding. Ligand binding in the tissue sections was measured by liquid scintillation counting after repeated washing of the coverslips. Elution of ligand binding proteins into the incubation buffer was quantitated with the dextran-coated charcoal method. Specific ligand binding was related to the total tissue protein content which was determined on parallel, unmounted sections. Scatchard analysis showed specific saturable and high affinity (Kd = 0.01-2 nM) section-bound and soluble binding sites in cryostat sections of calf uterus, human endometrium and breast cancer samples. Ligand specificity was studied by competition of [3H]R5020 with a 100-fold excess of various steroid receptor ligands. The competition was excellent for R5020 and progesterone, negligible for estrogens and slight for androgens and corticosteroids. These binding characteristics provide evidence that with this assay progesterone receptors are determined. Exchange experiments showed that with this method total, free as well as occupied, progesterone receptors can be measured. A highly significant linear correlation, and agreement in PR status classification between assay on cytosol and sections was obtained for a series of 21 breast cancer samples. Finally, progesterone receptor analysis using cryostat sections results in the recovery of 2-3 times more PR from the same amount of tissue as compared to the use of cytosol. These results indicate that progesterone receptors can be reliably assayed with Scatchard analysis using cryostat sections, which requires less tissue than the cytosol assay. This method, which is simple and easy to perform could be of practical importance, particularly when only small tissue samples (which also have to be analyzed morphologically or histochemically) are available and when quantitative radiochemical progesterone receptor data are required for direct comparison with (immuno-) histochemical information.

Radiochemical determination of estrogen receptors in cryostat sections of target tissues.

A radioreceptor assay on unfixed cryostat sections has been developed. Mounted and dried sections were incubated with radiolabeled estradiol in the absence and presence of an excess of diethylstilbestrol and washed with buffer. Binding of radiolabel to sections was measured by direct liquid scintillation counting. Also protein-bound radioactivity which eluted from the sections was determined with a dextran-coated charcoal assay. Parallel sections were used for histological staining and protein determination. Scatchard analysis showed the presence of specific saturable binding sites for estradiol with dissociation constants in the 0.1-1.5 nM range. It is concluded that these high affinity and limited capacity (type I) binding sites represent estrogen receptors. The ligand-binding activity of section-bound estrogen receptors did not decrease upon dry storage up to 20 h at 4 or 23 degrees C prior to assay. During aqueous incubation a significant amount of receptor, representing about 40-60% of the total tissue content, elutes from the sections. Steroid specificity was proven by incubation with excess androgen, progestogen or corticoid instead of diethylstilbestrol or estradiol. With these ligands no significant competition was found. Tissue specificity was demonstrated by a very low level of specific estradiol binding to cryostat sections of rat skeletal muscle, spleen and intestine and by a moderate level in rat liver.