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 US Food and Drug Administration (FDA) approval to treat hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced or metastatic breast cancer (MBC). Administrative claims data were used to describe patient characteristics and select clinical and economic outcomes in US patients treated in routine clinical practice. Prior analyses from electronic health records data indicate approximately 25% of patients received either palbociclib or ribociclib for MBC before initiating abemaciclib treatment; this work further explored these findings and associated outcomes. Methods This retrospective study analyzed medical and pharmacy claims from the IBM (R) MarketScan (R) Research Databases between 1 January 2007 to 31 January 2020. Patients with HR+, HER2- MBC newly initiating abemaciclib between 1 September 2017 and 31 October 2019 were included and grouped by concomitant therapy (+aromatase inhibitor (AI), +fulvestrant (F), 200 mg abemaciclib monotherapy (Mono), or +other), and outcomes were analyzed by prior CDK4 & 6i use. Patient and treatment characteristics were summarized with descriptive statistics. Kaplan-Meier methods assessed time-to-discontinuation (TTD; i.e., persistency) and time-to-chemotherapy (TTC). Adherence (defined by the medication possession ratio) and drug wastage were determined. Results This analysis included 454 patients (mean age 57.7 years), with 35.0% (n = 159) in the +F group, 29.3% (n = 133) in the +AI group, 10.4% (n = 47) in the 200 mg Mono group, and 25.3% (n = 115) in the +other group. Prior chemotherapy and CDK 4 & 6i use were present in 23.8% and 49.8% of all patients, respectively. Visceral metastases were present at abemaciclib initiation in 50.4% in the +AI group; 49.7% in the +F group; and 55.3% in the 200 mg Mono group. Liver metastases were present in 33.7% of the overall population. Among patients without prior CDK4 & 6i use, the median TTD for patients receiving abemaciclib + AI was not reached [95% CI 430-not reached (NR) days], abemaciclib + F [531 days (95% CI 281-NR)], and abemaciclib mono [141 days (95% CI 80-NR)]. Median TTC for abemaciclib + AI and abemaciclib + F groups were not reached and the median TTC for abemaciclib mono was 535 days (95% CI 181-NR). Medication adherence was 88.7% and medication wastage costs among those with at least one dose modification were $808.12 and $452.2 per patient per month based on amount paid and wholesale acquisition cost (WAC), respectively. Mean length of follow-up for all patients was 350 days (SD 187). Conclusion These real-world data complement clinical trial results by examining abemaciclib use among patients treated in routine clinical practice. The sizeable number of patients treated with prior CDK4 & 6i, chemotherapy, and/or visceral metastases at abemaciclib initiation suggest that many patients had very advanced disease and/or were in later stages of their treatment. These data confirm a higher percentage of patients treated with previous CDK4 & 6i than reported previously, reinforcing the importance of the ongoing, prospective clinical trials evaluating outcomes following progression on CDK4 & 6i.