STS and breast cancer: This has been supported by: (1) STS activity in liver, normal breast tissues, and breast cancer tissues is million fold higher than aromatase activity;8 (2) estrone produced from estrone sulfate through the STS pathway is about 10-fold higher than that produced from androstenedione through aromatase action;9 and (3) STS expression is a very essential prognostic factor in human breast carcinoma.10, 11 Thus, STS is an attractive target for the treatment of hormone-dependent breast,12 endometrial,13 prostate cancers, and endometriosis.14