Palbociclib (codenamed PD-0332991, trade name Ibrance) is a drug for the treatment of ER-positive and HER2-negative breast cancer developed by Pfizer. It is a selective inhibitor of the cyclin-dependent kinases CDK4 and CDK6.
Palbociclib was the first CDK4/6 inhibitor to be approved as a cancer therapy by any organization, and as of December 2017 has been prescribed more than 90,000 times