Terry L. Evans, MD, clinical assistant professor of medicine, University of Pittsburgh School of Medicine, UPMC Hillman Cancer Center, discusses the tolerability of CDK4/6 inhibitors in hormone receptor (HR)-positive breast cancer.

All 3 CDK4/6 inhibitors approved in breast cancer—–abemaciclib (Verzenio), palbociclib (Ibrance), and ribociclib (Kisqali)–– demonstrate similar efficacy, but their tolerability profiles differ, explains Evans. Abemaciclib may be a more potent inhibitor, he adds. In the phase III MONARCH-3 trial, abemaciclib was combined with fulvestrant, showing tumor shrinkage by RECIST criteria, something that is rarely seen with cytostatic drugs, says Evans.

In terms of side effects, palbociclib seems to be the safest of the 3 drugs. With ribociclib, there is a 3% to 4% incidence of QTc prolongation, which can trigger more serious heart conditions, Evans cautions. Abemaciclib is known to cause diarrhea, so patients with existing bowel issues should be warned that it may exacerbate that.

Terry L. Evans, MD

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Dr. Evans on the Tolerability of CDK4/6 Inhibitors in HR+ Breast Cancer