Distinction between malignant and normal breast tissue based on endogenous mediators of estradiol binding

A component of human breast tumors, isolated by chromatographing the cytosol on hydroxylapatite, increased specific estradiol binding by the cytosolic proteins (23/24) while a similarly isolated component of normal sections of the cancerous breasts inhibited sharply the binding (17/17). Using the same procedures, a component isolated from rat uteri excised at proestrus acted like the one from human breast tumors and a component isolated from uteri at the other phases of the cycle acted like the one from normal breast tissue. The described hormone binding differences are revealed in incubations at 37 degrees C with divalent copper present in the incubation mixture.