Lilly Announces Positive Overall Survival Results from Phase 3 monarchE Trial in High-Risk HR+, HER2- Early Breast Cancer

China Finance Network October 18th: Eli Lilly and Company announced yesterday that the primary analysis of overall survival (OS) in the Phase III monarchE trial showed that, in patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-), lymph node-positive, high-risk early breast cancer, two years of treatment with abemaciclib combined with endocrine therapy (ET) reduced the risk of death by 15.8% compared to ET alone. Additionally, this treatment regimen demonstrated sustained long-term benefits in invasive disease-free survival (IDFS) and distant relapse-free survival (DRFS).

The study results were presented as a late-breaking oral report on October 17, 2025, at the annual meeting of the European Society for Medical Oncology (ESMO) held in Berlin, Germany. These data are being submitted to regulatory authorities around the world.

Professor Stephen Johnston, MD, PhD, Professor of Breast Cancer Oncology and Consultant Medical Oncologist at The Royal Marsden Hospital, and principal investigator of the monarchE study, said that for patients, overall survival is the most important endpoint. Abemaciclib in combination with endocrine therapy is the first modern therapy to significantly improve overall survival in the adjuvant setting in over 20 years. These findings represent a significant advancement in the treatment of HR+, HER2− high-risk early breast cancer.

The data announced this time include the primary analysis results of overall survival (OS), with a median patient follow-up time of 6.3 years, of which more than 75% of patients were followed up for at least four years after completing two years of abemaciclib treatment. In the intent-to-treat (ITT) population, abemaciclib combined with endocrine therapy reduced the risk of death by 15.8% compared to endocrine therapy alone [7-year overall survival rate: 86.8% vs. 85.0%; hazard ratio HR=0.842; 95% CI: 0.722–0.981; two-sided P-value=0.027].

Moreover, at the seven-year analysis, abemaciclib combined with endocrine therapy demonstrated a sustained reduction in recurrence risk, continuing to show significant benefits and prolonged effects on invasive disease-free survival (IDFS) and distant relapse-free survival (DRFS) as presented in the five-year data from the monarchE study. Notably, compared with endocrine therapy alone, the proportion of patients with cancer metastasis decreased by 32% among those receiving abemaciclib plus endocrine therapy (6.4% vs. 9.4%). Long-term follow-up of this trial will help determine whether the sustained difference in the proportion of patients with cancer metastasis will translate into further enhancement of survival benefits over time.

Jacob Van Naarden, Executive Vice President of Eli Lilly and President of the Oncology Division, stated that these results demonstrate a significant reduction in the risk of recurrence for patients and an improvement in overall survival, marking a major advancement in the treatment of lymph node-positive, HR+, HER2− high-risk breast cancer. "These results further solidify the position of abemaciclib combined with two years of endocrine therapy as the standard treatment for lymph node-positive high-risk patients, bringing new hope to such patients."

Safety results were consistent with the known profile of abemaciclib and previous analyses from the monarchE study, with no new safety signals or delayed toxicities observed. In the monarchE study, the most commonly reported (≥5%) grade 3 or 4 adverse events in the abemaciclib group compared to the tamoxifen or aromatase inhibitor group were: neutropenia (19.6% vs 1%), leukopenia (11% vs <1%), diarrhea (8% vs 0.2%), and lymphopenia (5% vs <1%). As in previous analyses of the monarchE study, adverse events were generally managed through dose adjustments.

Sue Weldon, CEO of Unite for HER, stated: "These results are highly significant for patients with high-risk early-stage breast cancer. The latest research data show that this treatment can help more patients extend their survival, which is a major advancement for our patient community. During this Breast Cancer Awareness Month, we celebrate this milestone together, while remaining acutely aware that much work remains to ensure every eligible patient has the opportunity to benefit from life-changing therapies."