According to the preplanned overall survival interim analysis results of the monarchE trial, abemaciclib plus endocrine therapy continues to show a benefit in the reduction of risk of developing invasive and distant disease recurrence after completion of treatment among patients with HR-positive, HER2-negative, high-risk, eary breast cancer.

The open-label, phase 3 monarchE trial enrolled patients with HR-positive, HER2-negative high-risk early breast cancer, where high-risk was defined as having either ≥4 positive axillary lymph nodes, or 1 to 3 positive axillary lymph nodes with grade 3 disease and/or a tumor of ≥ 5 cm (Cohort 1, n = 5120). Additionally, Cohort 2 consisted of patients with 1 to 3 positive axillary lymph nodes and a central Ki67 ≥ 20% (n = 517). The intention-to-treat population included both Cohort 1 and Cohort 2. Patients were randomized on a 1-to-1 basis to receive either endocrine therapy alone or with abemaciclib for 2 years.

With a median follow-up duration of 54 months, abemaciclib continued to benefit patients for invasive disease-free survival (hazard ratio [HR], 0.680; 95% confidence interval [CI], 0.599 to 0.772) and distant relapse-free survival (HR, 0.675; 95% CI, 0.588 to 0.774). There was a 5-year absolute improvement in invasive disease-free survival rate of 7.6% and distant relapse-free survival rate of 6.7% with abemaciclib, compared to the respective rates of 6.0% and 5.3% at 4 years, and 4.8% and 4.1% at 3 years. The treatment benefit seen in Cohort 1 was consistent with the benefit seen in the intention-to-treat population. No new safety signals were reported and there continued to be fewer deaths in the abemaciclib plus endocrine therapy arm (n = 208) compared with the endocrine therapy arm (n = 234; HR, 0.903; P = .284). However, the threshold for significance was not met.

As study authors concluded, “abemaciclib plus [endocrine therapy] continued to reduce the risk of developing invasive and distant disease recurrence well beyond the completion of [treatment],” adding that the 5-year absolute improvement “further supports the use of abemaciclib” among patients with high-risk early breast cancer. They noted that overall survival data is continuing to evolve in favor of abemaciclib plus endocrine therapy and follow-up is ongoing.

Source:

Harbeck N, Rastogi P, O’Shaughnessy J, et al. Adjuvant abemaciclib plus endocrine therapy for HR+, HER2–, high-risk early breast cancer: Results from a preplanned monarchE overall survival interim analysis, including 5-year efficacy outcomes. Presented at JADPRO Live. November 15-17, 2024; Grapevine, TX. Poster: JL1201E