Real-world treatment outcomes of abemaciclib in older patients with HR+, HER2- metastatic breast cancer in Japan

To understand the real-world use of abemaciclib in older patients (≥65 years) with HR+, HER2- metastatic breast cancer (MBC) in Japan. This study retrospectively analyzed a Japanese administrative claims database for patients with HR+, HER2- MBC who received abemaciclib as the first CDK4/6 inhibitor (CDK4/6i) from November 2018 to May 2023. Patient characteristics and treatment patterns were summarized. Median time to discontinuation (mTTD) and chemotherapy-free survival (CSF) was estimated using Kaplan - Meier method. Among 3,699 abemaciclib-treated patients with HR+, HER2- MBC, 1,681 (45.4%) were ≥65 years old. Among these, abemaciclib + fulvestrant (55.0%) was the most common regimen. The mTTD (95% CI) of first abemaciclib therapy was 12.8 months (11.4-13.6). The overall mTTD (95% CI) with all the BC drugs after starting abemaciclib was 40.2 months (37.0-44.0). The median (95% CI) CFS after starting abemaciclib was 34.8 months (30.2-39.5). Among 1,149 older patients who discontinued the abemaciclib therapy, 897 (78.1%) patients received subsequent treatment. The most common first subsequent therapy was the endocrine therapy + CDK4/6i regimen (34.9%). This study indicated that abemaciclib regimens were feasible for older patients with HR+, HER2- MBC in Japan.