A prospective post-marketing observational study of abemaciclib in patients with HR+, HER2− breast cancer in China

BACKGROUND: Abemaciclib is approved for hormone-receptor positive (HR+), human epidermal growth factor receptor-2 negative (HER2-) locally advanced/metastatic breast cancer (ABC) and high-risk early BC (EBC) in China. This prospective observational study describes real-world abemaciclib safety and effectiveness among Chinese patients with HR+/HER2- EBC/ABC. METHODS: Adults with HR+/HER2- EBC/ABC who received abemaciclib between Mar-2022 and Jan-2024 across 32 Chinese centers were enrolled. Primary objective was to evaluate treatment-emergent adverse event (TEAE) and serious AE (SAE) incidence within 24 weeks of treatment. Secondary objective was to describe Week 24 event-free survival (EFS). RESULTS: Among 387 patients with EBC and 539 with ABC (median age: 50.0 and 55.0 years, respectively), 89.1% and 82.4% received 150 mg twice daily initially. Abemaciclib was combined with aromatase inhibitors in 95.6% (EBC) and 60.5% (ABC) patients, and fulvestrant in 38.0% (ABC). TEAEs occurred in 85.5% (EBC) and 81.8% (ABC) patients (commonly diarrhea, neutrophil count decreased, and white blood cell count decreased), and SAEs in 3.9% and 7.4%. AEs led to discontinuation in 4.4% (EBC) and 7.2% (ABC) patients. Diarrhea was the most common AE leading to discontinuation (2.1% [EBC] and 1.7% [ABC]). Most patients who discontinued treatment due to AEs had no dose modification, while most with dose reduction/interruption remained on abemaciclib. Week 24 EFS rates (95% CI) were 99.7% (97.6-100.0; EBC) and 85.1% (81.3-88.2; ABC). CONCLUSIONS: Real-world safety, tolerability, and effectiveness of abemaciclib in Chinese patients with HR+/HER2- EBC and ABC were consistent with clinical trials, with no new safety signals, supporting its positive real-world benefit-risk profile.