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William J. Gradishar, MD, FACP, FASCO


ESMO 2022: MONARCH 3 Survival Update on Abemaciclib-Based Therapy for Advanced Breast Cancer

By: Victoria Kuhr, BA
Posted: Wednesday, September 21, 2022

According to the second interim overall survival analysis from the phase III MONARCH 3 study, longer overall survival was reported in patients with hormone receptor (HR)-positive and HER2-negative advanced breast cancer with the addition of the CDK4/6 inhibitor abemaciclib to a nonsteroidal aromatase inhibitor in both the intent-to-treat population and the visceral disease subgroup. However, Matthew P. Goetz, MD, of the Mayo Clinic, Rochester, Minnesota, and colleagues observed neither group met the threshold for statistical significance for overall survival. These findings were presented at the European Society for Medical Oncology (ESMO) Congress 2022 (Abstract LBA15).

The previous MONARCH 2 study led to approval of the combination therapy abemaciclib and fulvestrant in patients with HR-positive and HER2-negative advanced breast cancer who experienced disease progression on prior endocrine therapy. The trial demonstrated significant overall survival benefit. MONARCH 3 led to the approval of abemaciclib plus an aromatase inhibitor as initial therapy for postmenopausal patients with HR-positive and HER2-negative advanced breast cancer. A second interim analysis of MONARCH 3 was scheduled after approximately 252 events in the intent-to-treat population. The data cutoff was July 2021.

A total of 493 patients were included in the second interim analysis. Of them, 328 patients received an aromatase inhibitor and abemaciclib, and 165 received the aromatase inhibitor alone. The median follow-up was 70.2 months. The intent-to-treat population given the abemaciclib-based therapy experienced a median overall survival of 67.1 months, compared with 54.5 months without abemaciclib. In the visceral disease subgroup, the the median overall survival was 65.1 months with the abemaciclib combination, compared with 48.8 months without abemaciclib. However, the results from treatment group were not considered significant.

The final overall survival analysis will be completed when at least 315 overall survival events in the intent-to-treat population and 189 in the subgroup visceral disease occur.

Disclosure: For full disclosures of the study authors, visit

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