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monarchE Continues To Show Abemaciclib Advantage For Invasive DFS

Adding abemaciclib to adjuvant endocrine therapy improves 2-year invasive disease-free survival for HR-positive, HER2-negative breast cancer patients with high-risk early disease
10 Dec 2020
Anticancer Agents;  Breast Cancer

Author: By Lynda Williams, Senior medwireNews Reporter 

 

medwireNews: Using the CDK4/6 inhibitor abemaciclib alongside adjuvant endocrine therapy achieves a significant improvement in invasive disease-free survival (IDFS) compared with endocrine treatment alone, confirm updated findings from the monarchE trial of early breast cancer patients with high-risk, hormone receptor (HR)-positive, HER2-negative disease. 

The primary outcome analysis, performed at a median follow-up of 19.0 months and after 395 IDFS events, was presented during the 2020 San Antonio Breast Cancer Symposium, confirming the positive results of the second preplanned interim analysis reported previously, after a median 15.5 months of follow-up. 

Priya Rastogi, from the University of Pittsburgh in Pennsylvania, USA, said that at data analysis, 25.5% of the trial participants had completed their 2-year course of abemaciclib 150 mg twice daily with standard adjuvant endocrine therapy (n=2808) or of endocrine therapy alone (n=2829), with the study treatments given after surgery and chemotherapy and/or radiotherapy. 

The participants all had four positive nodes or between one and three positive nodes with either grade 3 disease and/or a tumour at least 5 cm in diameter, or with a high Ki-67 status, defined as 20% or more tumour cells positive for the recurrent disease biomarker, she explained. 

At data cutoff, 163 IDFS events had occurred among the abemaciclib-treated patients and 232 among those given only endocrine therapy, giving a 28.7% risk reduction with the combination regimen that the presenter described as a “statistically significant and clinically meaningful improvement in IDFS.”  

This gave 2-year IDFS rates of 92.3% with the combined regimen versus 89.3% for adjuvant endocrine therapy alone. 

And analysis of the subgroup of 2498 Ki-67-high patients showed a significant 30.9% reduction in IDFS events with the addition of abemaciclib to adjuvant endocrine therapy, with 2-year rates of 91.6% versus 87.1% for patients given only adjuvant endocrine therapy.   

Among the whole cohort, patients given abemaciclib with their adjuvant endocrine therapy also experienced a statistically significant 31.3% reduction in the risk of distant relapse-free survival, with a 2-year rate of 93.8% versus 90.8% among controls. 

And monarchE follow-up continues until the final overall survival analysis is mature, Priya Rastogi said. 

Median duration of abemaciclib treatment was 17.3 months, and the combination and endocrine therapy-only arms had a comparable median duration of endocrine therapy of 18.3 and 18.7 months, respectively. 

“Safety was consistent with the known profile of abemaciclib and results from the second interim analysis”, commented Priya Rastogi, with “minimal increases” in the incidences of any-grade and grade 3 or higher treatment-emergent adverse events in the combination versus control arm, mainly grade 1 or 2 diarrhoea, fatigue and neutropenia.  

The majority (70.2%) of patients given abemaciclib had one or more dose holds, most commonly for adverse events (59.5%), such as diarrhoea (19.0%) and neutropenia (15.3%), while 42.5% had one or more abemaciclib dose reductions. 

“Most patients who required a dose hold or reduction were able to remain on study treatment”, said Priya Rastogi, adding that over half of patients who discontinued abemaciclib did so in the first 5 months of treatment, so there was a “steady decline” in the rate of discontinuation over time. 

“Abemaciclib in combination with endocrine therapy is the first CDK 4/6 inhibitor to demonstrate efficacy and tolerability for patients with HR-positive, HER2-negative, node-positive, high-risk early breast cancer”, she concluded. 

Reference 

Abstract GS1-01. O’Shaughnessy JA, Johnston S, Harbeck N, et al. Primary outcome analysis of invasive disease-free survival for monarchE: abemaciclib combined with adjuvant endocrine therapy for high risk early breast cancer. 2020 San Antonio Breast Cancer Symposium; 8–11 December. 

medwireNews (www.medwireNews.com) is an independent medical news service provided by Springer Healthcare. © 2020 Springer Healthcare part of the Springer Nature group

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