[Steroid sulfatase inhibitor].

More than 60 percents of breast cancers occur in post menopausal women and most of their initial stages are hormone dependent. For the treatment of estrogen dependent breast tumors, mainly two treatment tools are available, one is selective estrogen receptor modulator (SERM), and the other is aromatase inhibitor (AI). Although these drugs are clinically valuable, the existence of resistant tumors againt these two treatments is one of the most serious matters. The latest studies clarify that to inhibit the local formation of estrogen is more important than to decrease the estrogen dose in plasma. Steroid sulfatase (STS) is mainly expressed in local breast carcinoma tissues and is one of the most promising targets to inhibit the local formation of estrogens.