A CDK 4/6 inhibitor is a type of treatment that works to slow down cell growth and division by preventing certain proteins (called CDK 4 and CDK 6) from telling the cell that it needs to grow and divide.1,15 IBRANCE is a CDK 4/6 Inhibitor that does this in both healthy and cancer cells.1 This helps slow the progression of cancer, but it can also cause side effects, some of which are serious.1