skip to main content

CDK4/6 Inhibitor Toxicity — SCE Medical Oncology MCQ

Instant feedback + full explanation. One question, done properly.

ModerateBreast CancerCDK4/6 Inhibitor ToxicitySCE Medical Oncology

A 55-year-old woman with ER+/HER2- metastatic breast cancer on abemaciclib + fulvestrant develops persistent grade 2 diarrhoea (4-6 loose stools daily). This is a known class-specific adverse effect. What distinguishes abemaciclib from palbociclib and ribociclib regarding GI toxicity?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: D — Abemaciclib has higher CDK4-selectivity causing more frequent diarrhoea (~80% any grade) compared with palbociclib and ribociclib (~20-35%)

Abemaciclib has greater CDK4 selectivity (vs CDK6) compared with palbociclib and ribociclib, which correlates with its higher GI toxicity (diarrhoea in ~80% of patients). Management includes early loperamide initiation and dose reduction if persistent. Conversely, abemaciclib causes less neutropenia than palbociclib. This differing toxicity profile guides CDK4/6 inhibitor selection.

Reference: BNF Abemaciclib; ESMO 2024 MBC Guidelines; MONARCH trials