Real-world experience of abemaciclib for adjuvant and metastatic breast cancer.

Objective: Hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) breast cancer is the most common subtype. Abemaciclib, an inhibitor of cyclin-dependent kinases 4 and 6, was approved to reduce risk of recurrence in high-risk, HR+, HER2-, early breast cancer based on the monarchE trial. The most common adverse events reported in monarchE were diarrhea, neutropenia, and fatigue. Real-world tolerability data and incidence of adverse events with abemaciclib in the adjuvant setting versus the metastatic setting is lacking.

Data sources: This is a retrospective analysis of HR+, HER2- breast cancer patients on abemaciclib from March 2018 to September 2021 at Robert H. Lurie Comprehensive Cancer Center in Chicago, Illinois. Incidence, grade of adverse events, dose reductions, and discontinuations were evaluated in patients taking abemaciclib in the adjuvant setting and the metastatic setting.

Data summary: Of the 30 patients included in this analysis, 100% experienced an adverse event of any grade. During treatment, 12.5% treated in the adjuvant setting and 35.7% in the metastatic setting experienced grade ≥3 adverse events. Adverse events leading to discontinuation of abemaciclib occurred in 18.8% of patients in the adjuvant setting and 57.1% in the metastatic setting.

Conclusions: This data suggests abemaciclib is better tolerated in high-risk, HR+, HER2-, node-positive, early breast cancer treated in the adjuvant setting compared to the metastatic setting. Management of adverse events is crucial to help patients stay on therapy to improve clinical outcomes. Real-world tolerability of abemaciclib in both the adjuvant and metastatic settings is of importance.