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

Clinical and preclinical data support a significant role forinhibitors of the cyclin-dependent kinases (CDKs) 4 and 6in the treatment of patients with breast cancer. Recently,based on data showing improvement in progression-freesurvival, the use of palbociclib (Ibrance; Pfizer, Inc.) incombination with endocrine agents was approved totreat patients with hormone receptor-positive advanceddisease. Importantly, 2 other CDK4/6 inhibitors, abemaciclib(LY2835219; Lilly) and ribociclib (LEE011; Novartis),are in the late stage of clinical development. In this review,we will focus on clinical data on these 2 new drugs,highlighting their differences compared to palbociclib interms of single-agent activity, central nervous systempenetration, and common adverse events. In addition,we will present the ongoing clinical trials and discuss futuredirections in the field.