Inhibitory effect of mepitiostane on the growth of mammary tumor of a rat.

Mepitiostane (2alpha,3alpha-epithio-5alpha-androstan-17beta-yl 1-methoxycyclopentyl ether) is an orally active anti-estrogenic and anabolic-androgenic steroid compound. Mepitiostane administered orally suppressed the growth of transplanted estrogen-dependent mammary tumor in rats. This result was compared with the oral administration of fluoxymesterone, which is widely used orally for treatment of advanced breast cancer. Experimental result showed that Mepitiostane has a more dominant antitumor activity than fluoxymesterone. Therefore, this new compound may be useful for clinical treatment of breast cancer.