Abiraterone is a potent steroidal inhibitor against cytochrome P450 17alpha-hydroxylase-17,20-lyase (CYP17) with an IC50 at 4 nM. It was approved by the FDA in April 2011 to treat castration-resistant prostate cancer. A phase I/II clinical trial evaluating abiraterone acetate in advanced breast cancer patients are also underway. In preclinical studies, abiraterone has demonstrated the ability to selectively inhibit the target enzyme, resulting in inhibition of testosterone production in both the adrenals and the testes.