John Katzenellenbogen PhD, directs a research program that spans chemistry, biology, and medical applications with a particular focus on the action of estrogens in breast cancer and androgens in prostate cancer. He is recognized internationally as pioneer in the development of novel diagnostic and therapeutic agents for the management of hormone-regulated cancers, including the PET imaging agents FES for estrogen receptors in breast cancers and FDHT for androgen receptor in prostate cancers that are widely used in the clinical development of novel anti-hormones. He has also assisted in the development of a PET-based hormone challenge test that images hormone-induced changes in tumor metabolism and other molecular targets that is proving highly predictive of response to endocrine therapies in breast cancer. Through his extensive work elucidating the molecular details of estrogen action in various target tissues, he has designed novel estrogens that are being actively used to elucidate estrogen actions by numerous collaborators throughout the world. He has been honored as a Fellow of the American Academy of Arts and Sciences and is the recipient of numerous awards.