Additional follow-up is needed to determine whether adding abemaciclib to treatment with a nonsteroidal aromatase inhibitor (NSAI) can provide a significant improvement in overall survival (OS) for patients with hormone receptor-positive (HR+), HER2-negative advanced breast cancer, according to researchers.
A second interim analysis of the MONARCH 3 study showed a 12.6-month improvement in OS with abemaciclib, but this did not reach statistical significance. Follow-up is ongoing, and final OS results from this trial are expected in 2023.
The current results were presented at ESMO Congress 2022 by Matthew P. Goetz, MD, of the Mayo Clinic in Rochester, Minnesota.
MONARCH 3 (ClinicalTrials.gov Identifier: NCT02246621) is an international phase 3 trial that enrolled postmenopausal patients with HR+, HER2- advanced breast cancer. Patients were randomly assigned to receive an NSAI in combination with abemaciclib (n=328) or an NSAI plus placebo (n=165). The NSAI was anastrozole given at 1 mg daily or letrozole given at 2.5 mg daily. Abemaciclib was given at 150 mg twice daily.
In a prior analysis, abemaciclib significantly improved progression-free survival (PFS). The median PFS was 28.2 months in the abemaciclib arm and 14.8 months in the placebo arm (hazard ratio [HR], 0.540; 95% CI, 0.418-0.698; P =.000021). These data led to the global approval of abemaciclib for advanced breast cancer.
In the current analysis, the median follow-up was 5.8 years. The median PFS remained significantly improved with abemaciclib. The median PFS was 29.0 months in the abemaciclib arm and 14.8 months in the placebo arm (HR, 0.518; 95% CI, 0.415-0.648; P <.0001).
The researchers also found a numeric improvement in OS with abemaciclib, but this did not reach the threshold for significance. The median OS was 67.1 months in the abemaciclib arm and 54.5 months in the placebo arm (HR, 0.754; 95% CI, 0.584-0.974; P =.0301).
Similarly, for patients with visceral disease, there was a numeric improvement in OS with abemaciclib, but statistical significance was not reached. The median OS was 65.1 months in the abemaciclib arm and 48.8 months in the placebo arm (HR, 0.708; 95% CI, 0.508-0.985; P =.0392).
There was a trend toward improved OS with abemaciclib in almost all subgroups, particularly among patients who were progesterone-receptor negative (HR, 0.425; 95% CI, 0.257-0.702), those who had received prior aromatase inhibitor therapy (HR, 0.523; 95% CI, 0.329-0.832), and those with 1 organ involved at baseline (HR, 0.582; 95% CI, 0.349-0.970).
The final OS results from this trial are expected to be available in 2023 when at least 315 OS events will have occurred.
Disclosures: This research was supported by Eli Lilly and Company. Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.
Goetz MP, Toi M, Huober J, et al. MONARCH 3: Interim overall survival (OS) results of abemaciclib plus a nonsteroidal aromatase inhibitor (NSAI) in patients (pts) with HR+, HER2- advanced breast cancer (ABC). Presented at ESMO 2022; September 9-13, 2022. Abstract LBA15.