monarchE: 2-Year IDFS Benefit Confirmed For Clinicopathological High-Risk Breast Cancer Cohort

Author: By Lynda Williams, Senior medwireNews Reporter 

medwireNews: Subgroup findings for the monarchE trial confirm that women classified as having a high risk of breast cancer recurrence on the basis of clinicopathological features benefit from use of the CDK4/6 inhibitor abemaciclib alongside endocrine therapy (ET). 

Earlier analyses from the monarchE study have demonstrated an improvement in 2-year rates of invasive disease-free survival (IDFS) in the intention-to-treat (ITT) population, which included 5637 patients with hormone receptor-positive, HER2-negative early breast cancer at high risk of relapse, and in the subgroup of 517 patients whose high-risk classification was based on a high Ki67 score (cohort 2). 

At the ESMO Breast Cancer 2022 in Berlin, Germany, the investigators reported the efficacy findings for the 5120 patients in cohort 1 of the ITT population whose high-risk status was based on the presence of four or more positive axillary lymph nodes (ALNs) or between one and three ALNs alongside grade 3 disease and/or a tumour size of 5 cm or larger. 

These criteria are “familiar to breast oncologists and easily identified in the clinical practice”, explained Mattea Reinisch, from Kliniken Essen-Mitte in Germany. 

The patients were randomly assigned to receive abemaciclib 150 mg twice daily plus ET or ET alone for 2 years, followed by a 3–8-year period of ET as clinically indicated.  

At the time of the current analysis, patients had been followed up for a median of 28 months, and 8.4% of abemaciclib-treated patients and 8.5% of controls were continuing with treatment. 

The presenter reported a “clinically meaningful IDFS benefit in cohort 1” with a significant hazard ratio (HR) for events of 0.68 in favour of abemaciclib. After 2 years, there was a 3.0 percentage point absolute difference in IDFS between the abemaciclib and control arms (92.6 vs 89.6%) and this increased to 5.7 percentage points after 3 years (88.6 vs 82.9%). 

In addition, there was a “clinically meaningful” benefit in distant relapse-free survival (DRFS) with abemaciclib use, with a significant HR of 0.67. The absolute difference in this endpoint was 2.9 percentage points at 2 years (94.1 vs 91.2%) and 4.5 percentage points at 3 years (90.2 vs 85.7%).  

And Mattea Reinisch noted that “consistent benefit was observed across all subgroups of patient and disease characteristics” for both of the survival endpoints. 

She observed that the majority of first recurrences were distant metastases in both the abemaciclib and control arms but the rate for these was lower with use of the CDK4/6 inhibitor (71.9 vs 75.6%), especially those occurring in bone (62 vs 119 cases) and liver (42 vs 65 cases). 

“Consistent with the ITT population, cohort 1 demonstrates robust efficacy results, with clinically meaningful reduction in the risk of developing invasive disease, particularly incurable distant metastatic disease”, the investigator summarised. 

“The benefit of abemaciclib combined with ET in patients with HR-positive, HER2-negative early breast cancer at a high risk of recurrence was predominantly driven by cohort 1”, she added. 

“These data represent the first major advance in the treatment of this early breast cancer subtype in almost two decades which has recently received approval in the EU and Japan.” 

Discussing the presentation, Janice Wing-Hang Tsang, from The University of Hong Kong, noted that both IDFS and DRFS benefits associated with abemaciclib continued after treatment with the CDK4/6 inhibitor had ended. 

However, noting that most hormone receptor-positive breast cancer recurrences occur more than 5 years after treatment, she questioned whether abemaciclib use might also prevent late recurrences, and whether 2 years is the optimal duration of abemaciclib therapy. 

The discussant added that findings from the NATALEE trial of the CDK4/6 inhibitor ribociclib are now awaited and wondered whether this study would also show a IDFS benefit similar to monarchE or the negative results for the PALLAS trial of palbociclib. 

Reference 

Reinisch M, Toi M, Boyle F, et al. Adjuvant abemaciclib combined with endocrine therapy (ET): Efficacy results in monarchE cohort 1. Ann Oncol 2022;33(suppl_3):S148–S164. doi:10.1016/annonc/annonc889