977 – Dose adjustments and adherence to adjuvant abemaciclib in a brazilian real-world scenario

Abstract

Introduction: Abemaciclib combined with endocrine therapy is an established adjuvant treatment for high-risk hormone
receptor-positive (HR+), human epidermal growth factor receptor 2 (HER2)-negative early breast cancer. However, its prolonged use (up to two years) poses challenges related to tolerability and adherence, given the toxicity profile of CDK4/6
inhibitors. Common adverse events such as diarrhea, fatigue, and hematologic toxicity may lead to dose modifications or
discontinuation. Real-world data are important to better characterize treatment patterns and adherence.
Methods: This retrospective study evaluated patients with high-risk HR+ early breast cancer treated with adjuvant abemaciclib between 2019 and 2025 in Brazil. Key endpoints included initial dosing, treatment interruptions, dose reductions,
maintenance dosing, permanent discontinuation, and reasons for discontinuation.
Results: A total of 189 patients were included (median age 47 years; 58.7% premenopausal). Most tumors were stage II–III,
grade 2–3, and had Ki-67 expression ≥20%. Over half received neoadjuvant chemotherapy. Most patients (86.8%) received
aromatase inhibitors, and 53.9% had ovarian suppression. Nearly all patients (93.3%) initiated abemaciclib at the standard
dose (300 mg daily). At the time of analysis, 18.5% had completed the planned two years. Dose interruptions occurred in
27.6% and dose reductions in 43.1%. After dose adjustments, 58.2% maintained 300 mg daily, while others required lower
doses. Permanent discontinuation due to toxicity occurred in only 6.3%, typically after prior dose reductions. Grade ≥3
diarrhea and neutropenia occurred in 6.3% and 7.4%, respectively. Among patients with adherence data, 91.5% maintained
good adherence (≥70% of prescribed doses).
Conclusion: Dose modifications are common during adjuvant abemaciclib therapy in real-world practice. However, discontinuation rates are low, suggesting that proactive toxicity management with dose adjustments supports treatment
adherence. These findings reinforce the importance of close monitoring and individualized dosing strategies to maintain
treatment persistence without compromising efficacy in the adjuvant setting.
Ethics: Research Ethics Committee Approval (CAAE 73097723.1.0000.0087).