We have established or characterized six lines of human breast cancer maintained in long-term tissue culture for at least 1 year and have examined these lines for estrogen responsiveness. One of these cell lines, MCF-7, shows marked stimulation of macromolecular synthesis and cell division with physiological concentrations of estradiol. Antiestrogens are strongly inhibitory, and at concentrations greater than 3 × 10-7m they kill cells. Antiestrogen effects are prevented by simultaneous treatment with estradiol or reversed by addition of estradiol to cells incubated in antiestrogen. Responsive cell lines contain high-affinity specific estradiol receptors. Antiestrogens compete with estradiol for these receptors but have a lower apparent affinity for the receptor than estrogens. Stimulation of cells by estrogens is biphasic, with inhibition and cell death at concentrations of 17β-estradiol or diethylstilbestrol exceeding 10-7m. Killing by high concentrations of estrogen is probably a nonspecific effect in that we observe this response with 17α-estradiol at equivalent concentrations and in the otherwise unresponsive cells that contain no estrogen receptor sites.

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This is Paper 1 of a series on hormon-responsive human breast cancer cell lines in long-term tissue culture.

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