15 Concurrent Use of Abemaciclib and Radiation Therapy (RT) Among Patients With HR+, HER2– Metastatic Breast Cancer (MBC): Real-World Utilization and Safety

15 Concurrent Use of Abemaciclib and Radiation Therapy (RT) Among Patients With HR+, HER2– Metastatic Breast Cancer (MBC): Real-World Utilization and Safety15 Concurrent Use of Abemaciclib and Radiation Therapy (RT) Among Patients With HR+, HER2– Metastatic Breast Cancer (MBC): Real-World Utilization and Safety

Background

A substantial proportion of patients with hormone receptor– positive (HR+), HER2-negative (HER2–) metastatic breast cancer (mBC) require palliative radiation therapy (RT) for symptomatic disease management. However, real-world data on the tolerability of CDK4/6 inhibitors and concurrent RT are limited. This study aimed to describe real-world utilization and safety of concurrent abemaciclib (Verzenio) and RT use in patients with HR+,
HER2– mBC.

Methods

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

Results

The study included 174 women: The median age was 63.0 years (IQR, 54.0-71.0) years, and 8.0% had an ECOG performance status of 2 or greater at index. Overall, 31.0% had de novo mBC, 92.5% received care in community clinics, and the median follow-up time was 17.5 (IQR, 10.1-26.5) months. Prior to abemaciclib use, 20.1% and 28.2% of patients had chemotherapy or other CDK4/6 inhibitors, respectively. The median time from abemaciclib initiation to RT was 27.5 (IQR, 5.01-26.0) days and the duration of RT was 14.0 days. The most frequent RT sites were bone (64.4%), and the median RT dose was 30 Gy. About half of the patients (47.7%) received abemaciclib in combination with fulvestrant, and 76.4% initiated abemaciclib at 150 mg twice daily. During concurrent abemaciclib and RT use, 76.4% of the patients had no dose change in abemaciclib, 16.7% and 2.3% had a dose hold or dose reduction, respectively, and 4.0% discontinued abemaciclib. The incidence of select rwAEs was diarrhea (73.0%), fatigue (62.6%), rash (27.6%), and neutropenia (23.0%). The median (95% CI) TTD was 12.1 (9.5, 17.0) months, and overall, 24.1% discontinued abemaciclib therapy due to rwAEs.

Conclusion

In this retrospective cohort study, 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, a standard of care, is well tolerated in patients with HR+ HER2– mBC.