Abstract PS10-46: Real-world patient characteristics, utilization patterns, and outcomes of US patients with HR+/HER2- metastatic breast cancer treated with abemaciclib

Background Abemaciclib is the most recent oral cyclin-dependent kinase 4 and 6 inhibitor (CDK4&6i) to receive FDA approval to treat hormone receptor positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced or metastatic breast cancer (MBC). We used administrative claims data to describe patient characteristics, real-world utilization patterns, and outcomes in a US patient cohort upon initiating abemaciclib treatment for HR+, HER2- MBC.Methods This retrospective observational study analyzed medical and pharmacy claims from the IBM® MarketScan® Research Databases (Commercial and Medicare Supplemental) between 1-Jan-2007 to 31-Jan-2020. Patients (≥18 years) newly initiating abemaciclib between 1-Sept-2017 and 31-Oct-2019 were included if they had ≥2 breast cancer diagnoses, ≥2 secondary neoplasm diagnoses, evidence of HR+ disease, continuous enrollment ≥6 months before and ≥90 days after abemaciclib initiation (index date), and absence of therapies suggesting HER2 positivity. Patients were grouped by concomitant therapy (+aromatase inhibitor [AI], +fulvestrant [F], 200mg abemaciclib monotherapy [200mgMono], or +other), and stratified by prior CDK4&6i use (yes/no). Line of therapy (LoT) and reason for discontinuation were not able to be determined from this dataset. Baseline demographic, clinical, and treatment characteristics were summarized with descriptive statistics. Kaplan-Meier methods assessed time-to-discontinuation, defined as a gap of 60-days without an abemaciclib fill, following exhaustion of days’ supply from prior fills, or initiation of a different CDK4&6i (ie, palbociclib or ribociclib).Results There were 454 patients included in this analysis (mean [SD] age=57.7 years [10.8]; 98.9% female). Prevalence of new abemaciclib initiators was 29.3% (n=133) in the +AI group, 35.0% (n=159) in the +F group, 10.4% (n=47) in the 200mgMono group, and 25.3% (n=115) in the +other group. Prior CDK4&6i use within each regimen ranged from 37.6% (+AI) to 60.0% (+other). Visceral metastases were present in 50.4% in the +AI group; 49.7% in the +F group; 55.3% in the 200mgMono group; and 47.8% in the +other group. Nearly 75% (n=331) of all abemaciclib initiators began treatment with a 150 mg dose. Chemotherapy use in the 6-month pre-index period was observed for 18.8% in the +AI group; 21.4% in the +F group; 51.1% in the 200mgMono group; and 21.7% in the +other group. Median length of follow-up for all abemaciclib initiators was 321 days (IQR 195-482). Among those without prior CDK4&6i use, the median time-to-discontinuation for the +AI group was not reached (NR) (95% CI, 430 days-NR), the +F group was 531 days (95% CI, 281-NR), the 200mgMono group was 141 days (95% CI, 80-NR), and the +other group was 392 days (95% CI, 300-NR). In the subset with prior CDK4&6i use, the median time-to-discontinuation for the +AI group was 196 days (95% CI, 125-NR), the +F group was 146 days (95% CI, 93-225), the 200mgMono group was 140 days (95% CI, 86-NR), and the +other group was 191 days (95% CI, 113-280).Conclusion These real-world data complement pivotal abemaciclib clinical trial results by examining abemaciclib use among a more heterogeneous patient population in a clinical practice setting. The sizeable number of patients with prior CDK4&6i use, visceral metastases, and prior chemotherapy at abemaciclib initiation suggests many patients had very advanced disease and/or were in later stages of their treatment paradigm. Claims data lack many variables of clinical relevance needed to fully understand disease severity in the study population, such as LoT and degree of endocrine sensitivity; these limitations should be considered when interpreting CDK4&6i administrative claims studies. Citation Format: Kimberly R. Saverno, Julie Beyrer, Emily Nash Smyth, Hamad Abedtash, Angelo DeLuca, Yajun Emily Zhu, Sarah Rybowski. Real-world patient characteristics, utilization patterns, and outcomes of US patients with HR+/HER2- metastatic breast cancer treated with abemaciclib [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS10-46.