Dehydroepiandrosterone and 5-en-Androstene-3beta, 17beta-diol affect MCF-7 human breast cancer cell growth through estrogen receptor, as shown by Tamoxifen counteraction. To assess whether the aromatization of these adrenal androgens to classical estrogens is required to stimulate proliferation, we evaluated the aromatase activity of MCF-7 cells. Aromatase activity was determined in both whole cells grown as monolayer cultures and microsomal fraction of cell homogenates. The conversion of Androstendione to Estrone was very low in cell cultures. By contrast, a high aromatase activity was found in cell homogenates, indicating that in isolated microsomal fractions of MCF-7 cells aromatase is unveiled. Since in whole cultured MCF-7 cells the conversion of androgens to estrogens is negligible, we suggest that the stimulatory effect of DHEA and ADIOL on the 'in vitro' growth of MCF-7 does not involve the aromatase pathway.

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