The MONARCH 3 study

Prof Patrick Neven, oncological gynaecologist at the University Hospitals Leuven reports the updated overall survival data of the MONARCH 3 study.   

In this update on MONARCH 3, presented at SABCS 2023 by Matthew Goetz, the final overall survival data of this randomised controlled phase three trial were reported. The study included patients with endocrine-sensitive HER2-negative metastatic breast cancer who were randomised to receive either an aromatase inhibitor alone or an aromatase inhibitor plus abemaciclib, a CDK4/6 inhibitor.

After 8.1 years of follow-up, the results showed a clinically meaningful benefit in overall survival of 13.1 months. While this outcome was not statistically significant, the study’s limited sample size of 469 patients and the 2-to-1 randomisation ratio may have contributed to this result. Additionally, the six-year median progression-free survival was 23.1% in the combined group compared to 4% in the aromatase inhibitor alone group. Another notable finding was that the median time to the start of chemotherapy in the treatment sequence was delayed by 16.1 months, indicating a clinically meaningful impact of adding abemaciclib to an aromatase inhibitor.