Inhibitors of STS (STX64) and aromatase (anastrozole, letrozole) can block this intracrine formation of estrogens and, therefore, are used for clinical (aromatase inhibitors) or experimental (STS inhibitors) breast cancer therapy (Santen and Harvey, 1999; Stanway et al., 2007). This evidence concerns the gene CYP19A1 and breast carcinoma.