Background
Two years of adjuvant abemaciclib plus endocrine therapy is approved and guideline-recommended in patients with hormone receptor–positive/HER2-negative (HR+/HER2–), node-positive, early breast cancer at high risk of recurrence. In initial real-world studies, the high rate (> 85%) of treatment persistence beyond 3 months suggests that adjuvant abemaciclib is well-tolerated in routine clinical practice.This study describes 6-month treatment persistence and dosing patterns in patients with early breast cancer initiating abemaciclib 150 mg twice daily (BID).
Methods
Retrospective data were accessed from the US de-identified Flatiron Health Research Database. Adults with HR+/HER2–, node-positive, early breast cancer who initiated abemaciclib 150 mg BID from January 2022 to June 2024 were eligible. Data cut-off was December 2024. Persistence rate was the proportion of patients on abemaciclib for 6 months or more, allowing for 60-day or less medication gap within this period. Subgroup analyses were conducted in patients meeting the monarchE high-risk criteria (N2, N3, or N1 plus grade 3 and/or tumor ≥ 5 cm).
Results
Of 1063 eligible patients, the median age was 56 years (IQR 47, 65). Most had N1 (48%) or N2 (34%) disease. Median follow-up was 17.5 months (IQR 11, 25). Treatment persistence at 6 months was 75%. Discontinuation was mostly due to adverse events (AEs; 19%) and less than 1% due to recurrence. Approximately 50% of patients (n = 536) had 1 or more dose reductions. Persistence was 85% in patients with one or more dose reductions and 64% with no dose reductions. A total of 70% of patients who discontinued by 6 months did not have a dose reduction. Median time from start of abemaciclib to first dose change and/or hold was 49 days (IQR 23, 111). During the first 30 days of treatment and days 31 to 90, discontinuations due to AEs were lower in patients with dose reductions vs no dose reductions (0-30 days: 7% [overall], 1% [> 1 dose reduction], 12% [no dose reduction]; 31-90 days: 7%, 4%, 10%; 91-182 days: 5%, 6%, 5%). Persistence and use of dose reductions were similar in patients meeting the monarchE high-risk criteria.
Conclusion
In US clinical practice, 75% of patients who initiated adjuvant abemaciclib continued abemaciclib beyond 6 months. Treatment persistence was higher among patients with dose reductions vs those with no dose reductions, and rates of early discontinuations due to AEs were low in patients with dose reductions. Given that dose reductions in monarchE were not associated with reduced efficacy, these additional real-world data support the use of early-dose modifications to improve tolerability and treatment persistence for adjuvant abemaciclib in patients with high risk of recurrence.
Previously presented at SABCS 2025.
Study is sponsored by Eli Lilly and Company.
