Real-world treatment patterns and outcomes of abemaciclib for the treatment of HR + , HER2- metastatic breast cancer patients in Japan.

Introduction: This study described, in routine clinical practice in Japan, the patient characteristics, treatment patterns, and outcomes of female patients with HR + /HER2- metastatic breast cancer (MBC) who started abemaciclib treatment.

Methods: Clinical charts were reviewed for patients starting abemaciclib in 12/2018-08/2021 with a minimum of 3 months follow-up data post-abemaciclib initiation regardless of abemaciclib discontinuation. Patient characteristics, treatment patterns, and tumor response were descriptively summarized. Kaplan-Meier curves estimated progression-free survival (PFS).

Results: 200 patients from 14 institutions were included. At abemaciclib initiation, median age was 59 years, and the Eastern Cooperative Oncology Group performance status score was 0/1/2 for 102/68/5 patients (58.3/38.9/2.9%), respectively. Most had an abemaciclib starting dose of 150 mg (92.5%). The percentage of patients receiving abemaciclib as 1st, 2nd, or 3rd line treatment was 31.5%, 25.8%, and 25.2%, respectively. The most frequent endocrine therapy drugs used with abemaciclib were fulvestrant (59%) and aromatase inhibitors (40%). Evaluation of tumor response was available for 171 patients, 30.4% of whom had complete/partial response. Median PFS was 13.0 months (95% CI 10.1-15.8 months).

Conclusions: In a routine clinical practice setting in Japan, patients with HR + , HER2- MBC appear to benefit from abemaciclib treatment in terms of treatment response and median PFS, with the results broadly reflecting the evidence demonstrated in clinical trials.