Occupied and unoccupied oestradiol receptor in human breast tumour cytosol

Abstract

Occupied and unoccupied oestradiol receptors have been determined in cytosols from 84 primary breast tumours obtained at mastectomy. A solid phase hydroxylapatite (HAP) assay has been used. The assay was found to be simple and reliable and suited for routine use. Receptor was detected in 69% of the tumours. HAP assay of unoccupied receptor correlated very well with values obtained with a DCC assay ( R = 0.95), although the former method gave significantly lower results P < 0.01). However, the DCC assay seriously underestimated the total amount of receptor present in cytolols, particularly at low receptor concentrations. In eight tumours from premenopausal women, which were receptor negative with the DCC assay, significant amounts of occupied receptor could be detected. Seven of these contained progesterone receptor as well. Otherwise there seemed to be no obvious relation between amount of occupied receptor in the tumour and the presence of progesterone receptor. Unexpectedly, no significant difference was found in the concentration of occupied receptor in tumours from older and younger women, although the mean ratio of unoccupied to occupied receptor was much higher in the former (13.8 vs 1.49). It is concluded that the determination of total receptor will give a more accurate estimate of tumour receptor content than methods measuring unoccupied binding sites only. This would be particularly important in menstruating women, whose receptors may be masked by endogenous oestradiol.