Estrogen Receptors in Human Breast Cancer

Specific quantitative techniques have been used to measure the cytoplasmic estradiol-binding protein (EBP) in human mammary carcinoma tissue specimens. Sucrose gradient centrifugation reveals EBP to sediment at 8S and 4S. Variable quantities of non-specific estradiol binding occurs in the 4S region of the sucrose gradient necessitating controls to insure specificity of the estradiol protein interaction.

Using dextran-coated charcoal to separate bound from free estradiol Scatchard analysis finds the dissociation constant of the estradiol EBP interaction to be ∼ 2.6×10^-10 M, indicative of the very high affinity of the ligand for the EBP. Quantitation of EBP sites in 64 primary and metastatic human breast tumors demonstrates a continuous spectrum of values from 0 to 612 fmol per mg of cytoplasmic protein. Specific 8S binding in the sucrose gradient centrifugation was not detected in specimens containing less than 9.0 fmol EBP per mg cytoplasmic protein.

Since data from animal breast tumors and preliminary evidence from human breast tumors indicates an excellent correlation between the presence of abundant tumor EBP and endocrine-induced breast cancer regressions, precise quantitation of EBP in all human primary tumors may prove to be an excellent prognosticator of endocrine therapy in metastatic breast cancer.

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