Abemaciclib plus endocrine therapy for hormone receptor-positive, HER2-negative, node-positive, high-risk early breast cancer (monarchE): results from a preplanned interim analysis of a randomised, open-label, phase 3 trial

MonarchE is an open-label, randomised, phase 3 trial which recruited high risk hormone receptor positive, HER2 receptor negative, node-positive breast cancer patients (n=5637). Patients were randomised to receive standard of care 10 years of endocrine therapy +/- abemaciclib for 2 years. High risk disease was defined as 4 or more positive axillary lymph nodes, or between 1 to 3 positive axillary lymph nodes with grade 3 disease or tumour size >5cm. Additionally, further patients with one to 3 positive axillary lymph nodes and ki-67 >20% were also recruited. At 4 years, the invasive DFS was 85.8% in the abemaciclib + endocrine therapy group vs. 79.4% in the endocrine therapy alone group (HR 0.664; p<0.0001). At median follow up of 42 months, 5.6% of patients in the abemaciclib + endocrine therapy group died, as opposed to 6.1% in the endocrine therapy alone group (HR 0.929; P=0.5). The most common grade 3-4 adverse events were neutropenia, leukopenia, and diarrhoea with the addition of abemaciclib. Serious adverse event rate was 15.5% in the abemaciclib + endocrine therapy group vs. 9.1% in the endocrine therapy alone group. Therefore, adjuvant abemaciclib reduces recurrence risk in high risk hormone receptor positive, HER2 receptor negative breast cancer. Further follow up will determine whether this impacts on overall survival outcomes also.

Classifications: Adjuvant & Neoadjuvant Treatment

Keywords: Adjuvant treatment Endocrine therapy Trials