CDK4 and breast cancer: In a real-world study of 266 patients with breast cancer receiving CDK4/6 inhibitors, thromboembolic events including arterial and venous events were more frequent with palbociclib and ribociclib than with abemaciclib; however, palbociclib comprised the vast majority of CDK 4/6 inhibitors in the study, making comparisons between the agents challenging13.