Sucrose gradient centrifugation analysis was used to measure estradiol receptor levels in 35 patients with inoperable or recurrent mammary carcinomas that were subsequently treated with the antiestrogen tamoxifen (Nolvadex ICI). Carcinomas from eighteen patients demonstrated specific estradiol binding. Twelve of these patients responded to therapy. Seventeen patients had tumors without measurable estradiol binding. One of these responded to therapy. Tumors binding less than approximately 0.1 fmole of estradiol per μg DN.1 demonstrated a low response rate to tamoxifen ( 1 26). Electrofocusing of the estradiol receptor at pH 6.6 in polyacrylamide gel was found to be a quantitative and very sensitive method for the measurement of the estradiol receptor content in mammary carcinoma. Sixteen patients had their tumors analyzed with electrofocusing and all demonstrated some specific estradiol binding. The amount of estradiol binding in tumors from responders to tamoxifen or ovariectomy was approximately 20 times greater than the amount bound in tumors from non-responders. We conclude that there exists a positive correlation between the amount of specific estradiol binding in human mammary carcinomas and their response to subsequent antiestrogen therapy.
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