Tolerability and adherence to adjuvant abemaciclib in hormone receptor-positive, HER2-negative, node-positive high-risk early breast cancer: a real-world study.

BACKGROUND AND PURPOSE: Abemaciclib in addition to adjuvant endocrine therapy for hormone receptor positive (HR+) breast cancer improves disease free survival (IDFS) and overall survival (OS). However, treatment-related adverse events may lead to early discontinuation. Sahlgrenska University Hospital implemented a gradual increase in initial dosing, with the intention to improve tolerability and adherence. Patient/material and methods: This retrospective observational study described adherence, tolerability and healthcare utilization associated with a gradual dose increase of adjuvant abemaciclib. A total of 69 patients aged 31-81 years were treated at Sahlgrenska University Hospital between 1st of April 2023 and 1st of April 2025 with cut-off September 5th, 2025. Clinical encounters and treatment outcomes were extracted from medical records and analyzed using descriptive statistics. RESULTS: Patients were older and had worse Eastern Cooperative Oncology Group status compared with the monarchE registrational trial. At 12 and 26 weeks, 34 patients (49%) and 25 patients (36%) remained on the full dose of abemaciclib, respectively. Overall, 65 patients (94.2%) and 58 patients (84%) remained on treatment at any dose at 12 and 26 weeks. Treatment discontinuation was mainly driven by low grade adverse events (grade 1-2). During the study period 1069 clinical encounters were recorded; 15 patients (22%) had at least one emergency care encounter and seven (10%) required hospital admission. INTERPRETATION: The gradual dose increase strategy resulted in fewer patients maintaining the full dose at 12 weeks compared with monarchE and TRADE trials, while overall treatment persistence remained high. Treatment discontinuation was primarily driven by cumulative low-grade toxicity and healthcare utilization was considerable.