CDK4 and breast cancer: The overall ORR of 3.7% observed in this study was comparable to phase I trials of the other CDK4/6 inhibitors (Supplementary Table S8).2,4,6,8 Although dose-dependent, anti-tumor efficacy was not observed due to the small sample size, an analysis of PFS suggested that SPH4336 may be promising in the treatment of BC and sarcoma.