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

Clinical and preclinical data support a significant role for
inhibitors of the cyclin-dependent kinases (CDKs) 4 and 6
in the treatment of patients with breast cancer. Recently,
based on data showing improvement in progression-free
survival, the use of palbociclib (Ibrance; Pfizer, Inc.) in
combination with endocrine agents was approved to
treat patients with hormone receptor-positive advanced
disease. 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 in
terms of single-agent activity, central nervous system
penetration, and common adverse events. In addition,
we will present the ongoing clinical trials and discuss future
directions in the field.