CDK4 and sarcoma: Because it has been reported that CDK4R24C, an active mutant of CDK4, is present in human tumors (athough not reported in sarcomas) and cannot be inhibited by members of the INK4 family, we decided to overexpress this mutant in these sarcoma cells (Figure 2B) in order to gain insight on palbociclib mechanism by exploring the effect of CDK4R24C on its cellular response.