Effect of medroxyprogesterone acetate and norethisterone on the estradiol-stimulated proliferation of MCF-7 cells

We have investigated the effect of medroxyprogesterone acetate (MPA) and no rethisterone (NET) on the estradiol-stimulated proliferation of MCF-7 cells , a human breast cancer cell line. Applying the gestagens without estradiol , MPA caused a significant reduction in the proliferation of MCF-7 cells fr om 10(-9) to 10(-6) M while NET showed a significant increase in proliferat ion at the two highest concentrations used, 10(-6) and 10(-7) M. When the g estagens were combined with estradiol (10(-10) M), both showed a significan t concentration-dependent reduction in the proliferation of the MCF-7 cells . NET lost its proliferation stimulating effect and even became inhibitory when used in estradiol-stimulated MCF-7 cells. These data indicate that NET as well as MPA can inhibit the estradiol-stimulated proliferation of human breast cancer cells. Since in vivo MPA and NET are often used continuously combined with estradiol, the results may have clinical relevance when judg ing the potential of these gestagens for increasing the risk of breast canc er. Med Sci Res 27:595-596 (C) 1999 Lippincott Williams & Wilkins.