However, current chemotherapeutic breast cancer therapies usinginhibitors of the aromatase enzyme complex or selective estrogen receptormodulators (SERMs) often turn out to be unsatisfactory, resultingin high cancer relapse rates in patients.2−4 Notably, aromataseexpression has been found only in 60% of breast cancer cases, whilethe expression of steroid sulfatase (STS) has been detected in 90%of breast tumors.5 STS is a crucial enzymefor steroidogenesis. Here, CYP19A1 is linked to breast cancer.