Safety and efficacy of abemaciclib plus endocrine therapy in older patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative advanced breast cancer: an age-specific subgroup analysis of MONARCH 2 and 3 trials

Purpose Abemaciclib in combination with endocrine therapy (ET) has demonstrated significant efficacy benefits in HR+ , HER2- advanced breast cancer patients in the Phase 3 studies MONARCH 2 (fulvestrant as ET) and MONARCH 3 (letrozole or anastrozole as ET). Here, we report age-specific safety and efficacy outcomes. Methods Exploratory analyses of MONARCH 2 and 3 were performed for 3 age groups (<65, 65-74, and >= 75 years). For safety, data were pooled from both studies; for efficacy, a subgroup analysis of PFS was performed for each trial independently. Results Pooled safety data were available for 1152 patients. Clinically relevant diarrhea (Grade 2/3) was higher in older patients receiving abemaciclib + ET (<65, 39.5%; 65-74, 45.2%; >= 75, 55.4%) versus placebo + ET (<65, 6.8%; 65-74, 4.5%; >= 75, 16.0%). Nausea, decreased appetite, and venous thromboembolic events were all moderately higher in older patients. Neutropenia (Grade >= 3) did not differ as a function of age in the abemaciclib + ET arm (<65, 25.8%; 65-74, 27.4%; >= 75, 18.1%). Dose adjustments and discontinuation rates were slightly higher in older patients. Abemaciclib + ET improved PFS compared with placebo + ET independent of patient age, with no significant difference in abemaciclib treatment effect between the 3 age groups (MONARCH 2: interaction p-value, 0.695; MONARCH 3: interaction p-value, 0.634). Estimated hazard ratios ranged from 0.523-0.633 (MONARCH 2) and 0.480-0.635 (MONARCH 3). Conclusions While higher rates of adverse events were reported in older patients, they were manageable with dose adjustments and concomitant medication. Importantly, a consistent efficacy benefit was observed across all age groups.

Automated summary

The combination of abemaciclib with endocrine therapy has demonstrated significant efficacy benefits in HR+, HER2- advanced breast cancer patients, with improvement in PFS independent of patient age. While higher rates of adverse events were reported in older patients, they were manageable with dose adjustments and concomitant medication. Notably, a consistent efficacy benefit was observed across all age groups.