Background: Cyclin-dependent kinase (CDK) 4/6 inhibitor-based therapies have shown
great promise in improving clinical outcomes for patients with hormone receptor-positive (HR+),
human epidermal growth factor receptor 2-negative (HER2–) advanced breast cancer.
Objectives: 1. Discuss the mode of action of the three CDK4/6 inhibitors in late clinical development:
palbociclib (PD-0332991; Pfizer), ribociclib (LEE011; Novartis), and abemaciclib
(LY2835219; Lilly). 2. Describe the efficacy and safety data relating to their use in HR+, HER2–
advanced breast cancer. 3. Discuss the key side effects associated with CDK4/6 inhibitors along
with considerations for adverse event management and patient monitoring.
Method: Relevant information and data were assimilated from manuscripts, congress publications,
and online sources.
Results: CDK4/6 inhibitors have demonstrated improved progression-free survival in combination
with endocrine therapy compared with endocrine therapy alone. The side-effect profile of each
agent is described, along with implications for patient monitoring, and considerations for patient
care providers and pharmacists.
Conclusion: Addition of a CDK4/6 inhibitor to endocrine therapy increases efficacy and delays disease
progression. Insight into the unique side-effect profiles of this class of agents and effective patient
monitoring will facilitate the successful use of CDK4/6 inhibitor-based therapies in the clinic.