Cyclin-dependent kinase (CDK) 4/6 inhibitors have shown great results in numerous
clinical trials and have improved the clinical outcome for patients with
hormone-receptor-positive, human epidermal growth factor receptor 2-negative
advanced breast cancer significantly. To date, three CDK4/6 inhibitors are
approved by the US Food and Drug Administration (FDA): palbociclib, ribociclib
and abemaciclib; the first two compounds are aproved by the European Medicines
Agency (EMA) as well. In combination with endocrine therapy, all of them led to
significantly improved progression-free survival compared with endocrine therapy
alone. The aim of this article is to give an overview of the efficacy data and
to describe the CDK4/6 inhibitor-based treatment-associated adverse events,
including hematological and nonhematological adverse events. In addition, it
describes the corrrect approach to patient monitoring and adverse event
mangement and summarizes the current recommendations for dose reductions and
dose interruptions regarding the key adverse events, such as neutropenia,
diarrhea, QTc prolongation and hepatobiliary toxicity. Accurate patient
monitoring and management of the side effects is crucial, as several clinical
trials in early breast cancer are in progress and may lead to an additional
approval in the neo-/adjuvant setting.