Abemaciclib plus fulvestrant in treating hormone-receptor positive, HER2-negative advanced breast cancer-comparing real-world outcomes in England to the MONARCH-2 trial.

[BACKGROUND] Abemaciclib plus fulvestrant was approved in Europe following publication of the MONARCH-2 trial and recommended to enter the NICE Cancer Drugs Fund for HR+/HER2- advanced breast cancer. We aimed to assess MONARCH-2 generalisability to England clinical practice using real-world NHS trust data.

[METHODS] We identified patients receiving abemaciclib plus fulvestrant from April to December 2019 in the NHS England Blueteq and Systemic Anti-Cancer Therapy data, with follow-up to March 2024. We calculated overall survival (OS) from treatment initiation until death, and treatment-free survival (TFS) and chemotherapy-free survival (CFS) from initiation until post-discontinuation treatment or death (restricting CFS to chemotherapy). We measured outcomes using Kaplan-Meier methodology and compared to MONARCH-2.

[RESULTS] Median OS was 25.9 months [95% CI: 23.7, 28.4] (N = 876), compared to 46.7 months (N = 446) in MONARCH-2. Differences in gender, age and performance status did not explain OS differences. Median TFS was 11.6 months [95% CI: 10.3, 12.5] compared to a median PFS of 16.9 months in MONARCH-2. Median CFS was 15.3 months [95% CI: 13.8, 16.7], compared to 25.5 months in MONARCH-2.

[DISCUSSION] MONARCH-2 trial data are not generalisable to this real-world cohort, which had notably shorter OS, TFS and CFS that could not be explained by differences in measured patient characteristics.