Adding abemaciclib to adjuvant endocrine therapy (ET) can improve outcomes in patients with high-risk early breast cancer, according to results from the phase 3 monarchE trial.1 

Abemaciclib reduced the risk of an invasive disease-free survival (iDFS) event by 32% and reduced the risk of a distant relapse-free survival (DRFS) event by 33%, researchers found. These results were published in The Oncologist.

Researchers reported results from cohort 1 of the monarchE trial ( Identifier: NCT03155997). This cohort included 5120 patients with hormone receptor-positive, HER2-negative, early breast cancer. 

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All patients had high-risk features, which were defined as at least 4 positive axillary lymph nodes or 1-3 positive axillary lymph nodes with grade 3 disease and/or a tumor measuring at least 5 cm. 

At baseline, the patients had a median age of 51 years in both arms (overall range, 22-89 years), and 43.4% of patients in each arm were premenopausal. A majority of the patients had received adjuvant chemotherapy (58.7% in the abemaciclib arm and 58.6% in the ET-alone arm), and a minority had received neoadjuvant chemotherapy (36.5% and 36.3%, respectively).  

The patients were randomly assigned to receive adjuvant abemaciclib plus ET (n=2555) or ET alone (n=2565). Abemaciclib was given for 2 years, and ET was given for at least 5 years. 

The primary endpoint was iDFS. At a median follow-up of 28 months, abemaciclib significantly improved iDFS (HR, 0.68; 95% CI, 0.572-0.808; P <.0001). The 2-year iDFS rate was 92.6% with abemaciclib and 89.6% with ET alone. The 3-year iDFS rate was 88.6% and 82.9%, respectively.

DRFS was also significantly improved in the abemaciclib group (HR, 0.669; 95% CI, 0.554-0.809; P <.0001). The 2-year DRFS rate was 94.1% with abemaciclib and 91.2% with ET alone. The 3-year DRFS rate was 90.2% and 85.7%, respectively.

Safety data were not reported in this analysis but have been published previously.2

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.


1. Toi M, Boyle F, Im Y-H, et al. Adjuvant abemaciclib combined with endocrine therapy: Efficacy results in monarchE cohort 1. Oncologist. Published online November 7, 2022. doi:10.1093/oncolo/oyac234

2. Rugo HS, O’Shaughnessy J, Boyle F, et al. Adjuvant abemaciclib combined with endocrine therapy for high risk early breast cancer: Safety and patient-reported outcomes from the monarchE study. Ann Oncol. 2022;33(6):616-627. doi:10.1016/j.annonc.2022.03.006