Adding abemaciclib to endocrine therapy (ET) reduced the risk of disease recurrence in patients with early breast cancer, and that benefit persisted beyond the 2-year treatment period, according to updated results from the monarchE trial.

The results were presented at a recent European Society for Medical Oncology (ESMO) Virtual Plenary and simultaneously published in the Annals of Oncology.1,2  

On the basis of the new data, the US Food and Drug Administration (FDA) approved the use of abemaciclib with ET for adjuvant treatment in patients with hormone receptor (HR)-positive, HER2-negative, node-positive, early breast cancer at high risk of recurrence who have a Ki-67 score of at least 20%, as determined by an FDA-approved test.3

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“This is a major advance in the field of HR-positive breast cancer,” Aditya Bardia, MD, a medical oncologist at Massachusetts General Hospital in Boston who wasn’t involved in the research, said at the ESMO Virtual Plenary. “The last regulatory approval in the adjuvant hormone receptor-positive setting was more than 15 years ago.”

The phase 3 monarchE trial ( Identifier: NCT03155997) included 5637 patients with high-risk, node-positive, early-stage, HR-positive, HER2-negative breast cancer. Cohort 1 enrolled patients with 4 or more positive axillary lymph nodes (ALNs), or 1-3 positive ALNs and either grade 3 disease or a tumor size of 5 cm or larger. Cohort 2 enrolled patients with 1-3 positive ALNs and a high Ki-67 index (20% or higher).

All patients received physician’s choice of ET for at least 5 years. The patients were randomly assigned to receive ET alone (n=2829) or abemaciclib for the first 2 years (n=2808).

At baseline, the median age in both treatment arms was 51 years (range, 22-89 years). More than 99% of patients in each arm were women, and 43.5% in each arm were premenopausal. About 60% of patients in each arm had 4 or more ALNs, and about 34% had a low Ki-67 index (less than 20%).

Efficacy Outcomes

An interim analysis, conducted at a median follow-up of 15.5 months, when 12.5% of patients had completed the 2-year treatment period, revealed a significant improvement in invasive disease-free survival (IDFS) in patients receiving abemaciclib compared with those on ET alone.4

The new analysis, undertaken at regulators’ request, was based on a median follow-up of 27.1 months, when 72.2% of patients had completed the 2-year treatment period and 89.6% of patients were off study treatment.

The addition of abemaciclib continued to demonstrate an IDFS benefit (HR, 0.696; 95% CI, 0.588-0.823; P <.0001) and a distant recurrence-free survival (DRFS) benefit (HR, 0.687; 95% CI, 0.571-0.826; P <.0001).

At 3 years, the IDFS rate was 88.8% with abemaciclib and 83.4% with ET alone. The 3-year DRFS rate was 90.3% and 86.1%, respectively.

“With further follow-up, the [Kaplan-Meier] curves continued to separate, and the treatment benefit was maintained beyond the 2-year treatment period of abemaciclib,” said study investigator Joyce O’Shaughnessy, MD, a medical oncologist at Texas Oncology-Baylor Charles A. Sammons Cancer Center in Dallas, during the ESMO Virtual Plenary.