Factors influencing the estimation of oestrogen receptors in human malignant breast tumours

Abstract

Estimates of concentrations of binding sites ( P 0) and dissociation constants ( K d ) in extracts of human breast tumours had coefficients of variation of 16 and 29%. The sensitivity for P 0 was about 1 fmole per mg wet tissue. Samples taken from different areas of a tumour or from two tumours in the same breast showed significant differences in some cases. Freezing of cytosol preparations can cause deterioration. Oestrogen antagonists increased K d without affecting values of P 0, consistent with competition for oestrogen by binding to receptor with high dissociation constant. Sulphydryl reagents added to tissue supernatants increased P 0 in a few cases, and in one case exposed binding sites in a receptor-negative preparation. The presence of low-affinity binding components can lead to erroneous estimates of P 0 and K d of high-affinity receptors.