Abemaciclib Persistence in Patients with HR+, HER2-, Node-Positive Early Breast Cancer: a Real-World Analysis

Patients with node-positive, high-risk, hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) early breast cancer (EBC) can be treated with 2 years of abemaciclib plus endocrine therapy (ET) to improve invasive disease-free survival (IDFS; hazard ratio 0.68; absolute 7.6% 5-year IDFS benefit) over ET alone as observed in the monarchE trial. Most adverse events (AEs) from abemaciclib occurred early in treatment and could be managed with dose reductions while maintaining efficacy. Describing adjuvant abemaciclib dosing patterns and early treatment persistence in patients in a real-world node-positive EBC cohort provides new evidence on abemaciclib administration in clinical practice and may inform AE management.

Using the Flatiron Health Research Database de-identified data from October 2021 to February 2023, this retrospective study included patients aged ≥ 18 years with node-positive, HR+, HER2- EBC without prior CDK4/6 inhibitor exposure who initiated adjuvant abemaciclib at 150 mg twice daily (BID) and had ≥ 3 months follow-up. Dose modifications were identified. The persistence rate (%) and reasons for treatment discontinuation were described.

Among 354 patients (99.7% female), 88.1% of patients continued abemaciclib beyond 3 months. Dose reductions were observed in 50.8% of patients. Median time to first dose reduction was 59 days (IQR 35, 99). Of the patients with a dose reduction, 93.3% continued abemaciclib beyond 3 months. Among patients who discontinued abemaciclib because of AEs within 3 months of initiation without evidence of reinitiation (n = 40), 70.0% had no evidence of a dose reduction.

Eighty-eight percent of patients continued adjuvant abemaciclib beyond 3 months, demonstrating high early persistence and tolerance of abemaciclib in patients with node-positive EBC in a real-world clinical practice cohort. Persistence was 93.3% among patients who had a dose reduction, suggesting that timely dose adjustments, when needed, can promote early persistence on abemaciclib, particularly when patient-felt AEs are most frequent and can be effectively managed.