107P Results in Chinese patients from pre-planned overall survival interim analysis in monarchE: Abemaciclib plus adjuvant endocrine therapy for high risk HR+, HER2- early breast cancer

Abemaciclib (oral CDK4 and 6 inhibitor) plus endocrine therapy (ET) as adjuvant treatment demonstrated clinically meaningful improvement in invasive disease-free survival (IDFS) and distant relapse-free survival (DRFS) in Chinese patients (pts) with Hormone Receptor (HR+)-positive and human epidermal growth factor 2 (HER2)-negative high risk early breast cancer (EBC). This combination therapy provided sustained clinical benefits at the pre-planned overall survival interim analysis (OS IA2). Here we present the results of the subset of Chinese patients from monarchE at OS IA2. The overall study design was previously reported. Pts were randomized 1:1 to receive Abemaciclib + ET or ET alone. Eligible pts with ≥4 positive nodes, or 1-3 nodes and Grade 3 disease and/or tumor size ≥5 cm were included in Cohort 1 (C1); pts with 1-3 nodes and central Ki-67 ≥20% who did not meet entry criteria for C1 were included in Cohort 2 (C2). Analyses were conducted in Chinese pts enrolled from Mainland China, Hong Kong, and Taiwan in the intent-to-treat (ITT) population (501 pts), consisting of C1 (440 pts) and C2 (61 pts). At the time of data cutoff (July 1, 2022), all Chinese pts were off treatment with median follow-up of around 41 months. Sustained benefits of IDFS (HR=0.563, 95%CI: 0.343-0.923) and DRFS (HR=0.586, 95%CI: 0.341-1.006) were observed in Chinese pts in the ITT, with clinically meaningful improvement in the 4-year IDFS rates (88.5% vs 79.6%) and DRFS rates (90.0% vs 82.4%). In C1, the HR for IDFS was 0.582 (95%CI: 0.351-0.965) and DRFS was 0.610 (95%CI: 0.350-1.063), and a consistent benefit of abemaciclib was observed regardless of Ki-67 index. There were limited events of deaths in Chinese pts (abemaciclib plus ET vs ET: 6 [2.3%] vs 5 [2.1%]). No new safety signals were observed in Chinese pts. Consistent with reported results for the overall ITT population, abemaciclib combined with ET demonstrated clinically meaningful and sustained IDFS and DRFS benefits among Chinese pts with HR+, HER2-, high risk EBC and continued separation of the IDFS and DRFS curves. The OS data remain immature and follow-up is ongoing.