Utilization and Safety of Concurrent Use of Abemaciclib and Radiation Therapy Among Patients With HR+, HER2− Metastatic Breast Cancer in the Real-World Setting

TL;DR

This study examines how well patients with a specific type of breast cancer tolerate radiation therapy and abemaciclib together in real-world settings.

Contribution

The study provides real-world evidence on the safety and tolerability of concurrent abemaciclib and radiation therapy in HR+, HER2− metastatic breast cancer patients.

Findings

Most patients did not need dose modifications when using abemaciclib and radiation therapy together.

Common side effects included diarrhea, fatigue, rash, and neutropenia, but most were manageable.

Abstract

Real-world data on tolerability of concurrent radiation therapy (RT) and abemaciclib are limited. This study described real-world utilization and safety of concurrent RT and abemaciclib in patients with hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2−) metastatic breast cancer (MBC).

This retrospective study accessed data from the Flatiron Health United States nationwide deidentified electronic health records-derived longitudinal database. Abemaciclib initiation date was the index date (September 2017-September 2021). Concurrent RT was defined as receipt of any RT with ≥1 day of overlap with abemaciclib therapy. The minimum follow-up time was 90 days. Patient characteristics, treatment patterns, and real-world adverse events (rwAEs) were presented descriptively; Kaplan–Meier methods were used to assess time to treatment discontinuation.

This study included 174 female patients with a median follow-up time of 17.5 (IQR, 10.1-26.5) months. The median age was 63.0 (IQR, 54.0-71.0) years, 8.0% had Eastern Cooperative Oncology Group Performance Status ≥ 2 at index and 31.0% had MBC. Prior to abemaciclib use, 20.1% and 28.2% of patients had chemotherapy or other CDK4/6 inhibitors, respectively. About half of the patients (47.7%) received abemaciclib in combination with fulvestrant, and 76.4% initiated abemaciclib at 150 mg twice daily. Overall, 151 patients (86.8%) initiated RT at or after initiation of abemaciclib. During concurrent RT and abemaciclib use, 76.4% of patients had no dose change in abemaciclib; 16.7% and 2.3% had a dose hold or dose reduction, respectively; 4.0% discontinued abemaciclib. The incidence of rwAEs during concurrent abemaciclib + RT were diarrhea (73.0%), fatigue (62.6%), rash (27.6%), and neutropenia (23.0%). The median (95% CI) time to treatment discontinuation was 368 (290-516) days.

Most patients did not require a dose modification or interruption with concurrent RT and abemaciclib. These findings suggest that the addition of RT to abemaciclib therapy is well tolerated in patients with HR+, HER2− MBC.

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