CDK4 and breast carcinoma: First, there is conflicting data for CDK4/6 inhibitor use in early stage breast cancer—two large phase III trials with adjuvant palbociclib (i.e., PALLAS31 and PENELOPE-B32) reported negative results, while the phase III trials of adjuvant abemaciclib and ribociclib (i.e., MONARCHE33 and NATALEE30) were positive.