Pharmacokinetic Model of Abemaciclib: Correlation With Severe Diarrhea as the Primary Toxicity Endpoint in Patients With Localized Hormone Receptor-positive Breast Cancer

Remarkable progress has recently been made in the treatment of locally advanced, hormone receptor-positive, HER2-negative breast cancer with a high risk of recurrence, thanks to the addition of abemaciclib to endocrine therapy. This combination has led to a significant improvement in invasive disease-free survival. However, despite the combination's acceptable safety profile, 38% of patients experience grade 3 or higher diarrhea, and 23% experience grade 3 or higher neutropenia. This toxicity can lead to the premature discontinuation of treatment, limiting the benefits of this molecule. As with all oral therapies, the pharmacokinetics of abemaciclib lie at the intersection of efficacy and toxicity and can be modified by several external factors. The hypothesis of the study is that abemaciclib's toxicity is correlated with its plasma levels and that its concentration is modified by certain patient characteristics. To this end, a pharmacokinetic model of abemaciclib could be developed using a prospective, multicenter, real-world blood dosage study. This study will describe the relationship between abemaciclib concentration and diarrhea and severe neutropenia, as classified by CTCAE, as well as potential clinical and drug interactions. It is hoped that this model demonstrates the importance of monitoring abemaciclib concentrations. This could lead to a therapeutic trial in which the abemaciclib dose is adjusted according to concentration to limit toxicity while maintaining efficacy.

NCT Number	NCT07490509
Lead Sponsor	Poitiers University Hospital
Conditions	Abemaciclib, Abemaciclib-related Diarrhea, Breast Cancer
Enrollment	235 participants
Start Date	2026-09
Primary Completion	2029-09 (estimated)
Study Completion	2029-09 (estimated)
Updated on ClinicalTrials.gov	2026-07-21