Nuclear Estradiol-binding Sites in Human Breast Cancer1

The binding of estradiol to nuclear fractions extracted from human breast carcinomatous tissue was demonstrated. The material, which was extracted with KCI, had an approximate molecular weight of 37,000 and bound estradiol with both high and low affinity (K^ = 1 nM, type A receptors; K¿& 30 nw, type B receptors) as calculated according to the method of Scatchard. Competition studies indicated that both components were spe cific for estradiol, and among the 134 tumors studied the recep tors were found to be linked in almost all cases. Thirty-six % of the tumors were nuclear receptor positive. Cytoplasmic estradiol and progesterone receptors were also measured. Among the cytoplasmic tumors positive for cytoplasmic and progesterone receptors, 37% were devoid of both types of nuclear receptors; this may explain the failure of endocrine therapy in some cases. The determination of nuclear binding sites in human breast tumors appeared to be an interesting criterion for the assessment of estradiol-dependent cell growth.