Oestrogen receptor assay. False positive analysis?

The influence of unlabelled oestradiol, DES, testosterone and R-5020/org 2058 on tritiated oestradiol binding was investigated in 162 ER positive cases of patients with primary breast carcinoma. A dextran-coated charcoal as well as a sucrose gradient method was applied. In 122 cases only unlabelled oestradiol and DES significantly displaced the binding of labelled oestradiol. In the remaining 40 cases, oestradiol, DES, as well as testosterone and R-5020/org 2058 were able to displace the high-affinity, saturable binding of tritiated oestradiol equally. Possible explanations of this new discovery are discussed.