Treatment patterns after first-line abemaciclib therapy in patients with HR+, HER2- metastatic breast cancer in Japan.

AIMS: To determine treatment patterns following first-line abemaciclib therapy in patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+, HER2-) metastatic breast cancer in Japan. METHODS: This retrospective observational study used a Japanese administrative claims database to identify patients with HR+, HER2- metastatic breast cancer who received first-line abemaciclib between November 2018 and March 2024. Patient characteristics and treatment patterns were summarized. Time to treatment discontinuation (TTD) was estimated by Kaplan-Meier analysis. RESULTS: Among 3057 patients who received first-line abemaciclib, 520 received a second-line cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) (244 received abemaciclib and 276 received palbociclib) and 248 received endocrine monotherapy. Patients who received first-line abemaciclib plus a nonsteroidal aromatase inhibitor (NSAI) and second-line CDK4/6i had numerically longer median overall TTD (53.0 months) than those who received other second-line regimens (45.5 months). Patients who received first-line abemaciclib plus NSAI and second-line abemaciclib plus fulvestrant had numerically longer median second-line TTD (7.5 months) than those who received second-line fulvestrant monotherapy (4.0 months). CONCLUSIONS: Abemaciclib as both first- and second-line therapy was associated with sustained treatment duration in Japanese patients. Particularly, first-line abemaciclib plus NSAI followed by second-line abemaciclib plus fulvestrant may be a clinically meaningful treatment option.