CDK4 and breast carcinoma: Additionally, the difference in outcomes for the respective phase III CDK4/6i trials in early breast cancer (no significant benefit for palbociclib [PALLAS, PENELOPE-B]; significant benefit for ribociclib [NATALEE], abemaciclib [MonarchE]) further suggest that results observed for palbociclib may not be relevant for the other approved CDK4/6is [21–26].