At 4 years of follow-up, there was a meaningful increase of improvement in invasive disease-free survival and distant relapse-free survival benefit derived from adjuvant abemaciclib added to endocrine therapy for patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2 negative (HER2-), node-positive, high-risk early breast cancer that lasted beyond completion of treatment with abemaciclib, according to results from a phase 3 trial.

Data from the preplanned interim analysis of the monarchE trial were presented on Tuesday, December 6, 2022, at the San Antonio Breast Cancer Symposium in San Antonio, Texas, by first author Stephen Johnston, MBBS, The Royal Marsden Hospital, London, United Kingdom.

This trial included 5637 patients with high-risk early breast cancer classified into 2 cohorts. Cohort 1 (n = 5120) included patients with either ≥4 positive axillary lymph nodes or 1-3 axillary lymph nodes with either grade 3 disease and/or a tumor ≥5 cm. Cohort 2 (n = 517) included patients with 1 through 3+ positive axillary lymph nodes and a central Ki-67 index ≥ 20%. All patients were randomized on a 1-to-1 basis to receive endocrine therapy for up to 10 years either with or without abemaciclib for 2 years, during the study treatment period.

The median follow-up duration was 42 months, with all patients completing abemaciclib treatment. Dr Johnston and colleagues noted the invasive disease-free survival and distant relapse-free survival “illustrate a sustained benefit beyond the treatment period.” At 4 years, the invasive disease-free survival rate was 85.8%, an improvement of 6.4% from the 2-year rate of 79.4%. The distant relapse free-survival rate was 82.5%, an improvement of 5.9% from the 2-year rate of 82.5%. Though the overall survival remained immature, a lower number of deaths was reported in the abemaciclib arms compared to the endocrine therapy alone arm (5.6% vs 6.1% respectively; hazard ratio [HR] 0.929; 95% confidence interval [CI], 0.748 to 1.153; P = .503) suggesting a survival signal which favors abemaciclib. In Cohort 1, having a Ki-67 index ≥20% was associated with a worse prognosis, though abemaciclib treatment effects were observed regardless of Ki-67 index.

“The clinically meaningful benefit of adjuvant abemaciclib added to [endocrine therapy] in HR+, HER2-, node-positive, high-risk [early breast cancer] persists beyond completion of abemaciclib therapy, yielding an increase in absolute [invasive disease-free survival] and [distant relapse-free survival] benefit at 4 years,” study authors concluded.

Source:

Johnston S, Toi M, O'Shaughnessy J. “GS1-09: Abemaciclib plus endocrine therapy for HR+, HER2-, node-positive, high-risk early breast cancer: results from a pre-planned monarchE overall survival interim analysis, including 4-year efficacy outcomes.” Presented at San Antonio Breast Cancer Symposium; December 6 – 10, 2022; San Antonio, Texas. Abstract GS1-09