Palbociclib, sold under the brand name Ibrance among others, is a medication for the treatment of HR-positive and HER2-negative breast cancerdeveloped by Pfizer. It is a selective inhibitor of the cyclin-dependent kinasesCDK4 and CDK6.[1][2] Palbociclib was the first CDK4/6 inhibitor to be approved as a cancer therapy.[3] Mechanism of action Further information: CDK inhibitor It is a selective inhibitor of the cyclin-dependent kinases CDK4 and CDK6.[1][2] In the G1 phase of the cell cycle, mammalian cells…