Supplementary Material for: Clinical Development of the CDK4/6 Inhibitors Ribociclib and Abemaciclib in Breast Cancer

<div>Clinical and preclinical data support a significant role for</div><div>inhibitors of the cyclin-dependent kinases (CDKs) 4 and 6</div><div>in the treatment of patients with breast cancer. Recently,</div><div>based on data showing improvement in progression-free</div><div>survival, the use of palbociclib (Ibrance; Pfizer, Inc.) in</div><div>combination with endocrine agents was approved to</div><div>treat patients with hormone receptor-positive advanced</div><div>disease. Importantly, 2 other CDK4/6 inhibitors, abemaciclib</div><div>(LY2835219; Lilly) and ribociclib (LEE011; Novartis),</div><div>are in the late stage of clinical development. In this review,</div><div>we will focus on clinical data on these 2 new drugs,</div><div>highlighting their differences compared to palbociclib in</div><div>terms of single-agent activity, central nervous system</div><div>penetration, and common adverse events. In addition,</div><div>we will present the ongoing clinical trials and discuss future</div><div>directions in the field.</div>