Differential effects of progestogens on breast cancer cell lines.

Our in vitro results indicate that not all progestogens act equally on breast cancer cells. Some progestogens (medroxyprogesterone acetate (MPA), norethisterone acetate (NETA) and dienogest) alone or combined with estradiol (E2) stimulate proliferation of breast cancer cells, while others (dihydrodydrogesterone (DHD), the active metabolite of dydrogesterone, tibolone and progesterone (Prog)) alone or combined with estradiol induce apoptosis. Further pharmacological and clinical studies should be initiated to evaluate these findings in vivo.