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Abstract P1-19-10: Safety and efficacy of abemaciclib plus endocrine therapy (ET) in elderly patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+, HER2-) advanced breast cancer: An age-specific subgroup analysis of MONARCH 2 and 3 trials

Background: Breast cancer incidence and mortality rates are increased in patients’ older than 65 years. However, there are limited reports on age-specific efficacy, safety, and drug tolerability, particularly in elderly patients older than 75 years old. Abemaciclib demonstrated clinically meaningful progression-free survival (PFS) improvement in combination with endocrine therapy (ET) in HR+, HER2- advanced breast cancer patients in the Phase 3 studies, MONARCH 2 and 3. Here we report exploratory subgroup analyses of MONARCH 2 and 3 to provide age-specific outcomes. Methods: In MONARCH 2 (NCT02107703), patients progressing while on prior ET received abemaciclib (or placebo) plus fulvestrant; in MONARCH 3 (NCT02246621), postmenopausal women with no prior systemic therapy for recurrent or metastatic breast cancer received abemaciclib (or placebo) plus letrozole or anastrozole. Exploratory outcome analyses of MONARCH 2 and 3 studies were performed for three age groups (women aged Results: Pooled safety data were available for 1152 patients treated in MONARCH 2 and 3 trials, including 59.7% pts Conclusion: Abemaciclib in combination with ET demonstrates a tolerable safety profile and consistent efficacy benefit across all age subgroups examined, supporting the use of this combination in elderly patient populations. Despite the limited number of patients in the ≥75 group with potentially confounding comorbidities, the safety data suggest that patient education and appropriate management of toxicities, including dose adjustments and use of supportive medication for gastrointestinal toxicities, could maximize the benefit of abemaciclib. Citation Format: Matthew P. Goetz, Meena Okera, Hans Wildiers, Mario Campone, Eva-Maria Grischke, Luis Manso, Valerie Anne Marie Andre, Amy Lee Chong, Belen San Antonio, Masakazu Toi, George W Sledge Jr. Safety and efficacy of abemaciclib plus endocrine therapy (ET) in elderly patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+, HER2-) advanced breast cancer: An age-specific subgroup analysis of MONARCH 2 and 3 trials [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-19-10.