Abstract P5-21-02: Efficacy and safety of abemaciclib in patients with liver metastases in the MONARCH 1, 2, and 3 studies

Background: Abemaciclib is an oral, selective inhibitor of cyclin-dependent kinases 4 & 6 that is dosed on a twice daily continuous schedule. In patients (pts) with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC), abemaciclib has demonstrated clinical efficacy with a tolerable safety profile when administered as monotherapy in MONARCH 1 (NCT02102490), in combination with fulvestrant in MONARCH 2 (NCT02107703), and in combination with non-steroidal aromatase inhibitors (NSAI) in MONARCH 3 (NCT02246621). Inducing tumor response and delaying disease progression is of critical need in pts with liver metastases (mets). Methods: An exploratory subgroup analysis was conducted in pts with liver mets at baseline across the MONARCH 1, 2, and 3 studies. All pts had HR+, HER2- ABC. The primary endpoint of MONARCH 1 was objective response rate (ORR), and the primary endpoint of MONARCH 2 and 3 was investigator-assessed progression-free survival (PFS). Analysis methods for these endpoints were previously described. Key enrollment criteria and dosing information are listed in Table 1. Results: Efficacy results of pts with liver mets are described in Table 2. The most frequent adverse events observed in pts with liver mets in MONARCH 1 were diarrhea, nausea, and fatigue and in the abemaciclib arms of MONARCH 2 and 3 were diarrhea, neutropenia, and nausea. Conclusions: The results suggest that the combination of abemaciclib and endocrine therapy was an effective treatment option in pts with liver metastases, a population deriving modest benefit from single-agent endocrine therapy. Tolerability results were generally consistent with the safety populations previously reported for each study. Citation Format: Di Leo A, Dickler M, Sledge GW, Toi M, Forrester T, Nanda S, Koustenis A, Bourayou N, Johnston S. Efficacy and safety of abemaciclib in patients with liver metastases in the MONARCH 1, 2, and 3 studies [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P5-21-02.