Orally active, potent aromatase (CYP19) inhibitor (IC50 values are 0.4 and 0.12 nM at rat ovary and human placenta cells respectively) that only weakly inhibits the synthesis of other steroid hormones. Reduces plasma estrogen levels into ranges induced by ovariectomy and inhibits testosterone-induced breast cancer cell growth in vitro (IC50 = 0.13 nM).