The following article features coverage from the 2021 American Society of Clinical Oncology (ASCO) Annual Meeting. Click here to read more of Cancer Therapy Advisor‘s conference coverage.

Adding abemaciclib to adjuvant endocrine therapy (ET) produced “clinically meaningful” benefits in patients with hormone receptor-positive (HR+), HER2-negative, high-risk early breast cancer who had received neoadjuvant chemotherapy (NAC), according to results presented at the 2021 American Society of Clinical Oncology (ASCO) Annual Meeting.

The results are from an analysis of data from the phase 3 monarchE trial ( Identifier: NCT03155997) and were presented in a poster discussion by Miguel Martin, MD, PhD, of Hospital General Universitario Gregorio Marañón in Madrid.

Dr Martin and colleagues compared abemaciclib plus adjuvant ET with ET alone in patients with HR+, HER2-negative, high-risk early breast cancer who had received NAC.  

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The patients had 4 or more positive axillary lymph nodes, or they had 1 to 3 positive axillary lymph nodes and met at least one of the following criteria: grade 3 disease, tumor size of at least 5 cm, and central Ki-67 of at least 20%.

In all, there were 2056 patients who had received NAC. In this group, 1025 patients received abemaciclib plus ET, and 1031 received ET alone. For most patients (88.1% in the abemaciclib group and 90.3% in the ET group), NAC consisted of an anthracycline and a taxane.

Results showed that abemaciclib plus ET produced a benefit in invasive disease-free survival (IDFS) compared with ET alone. The 2-year IDFS rates were 87.2% and 80.6%, respectively (hazard ratio [HR], 0.614; 95% CI, 0.473-0.797; P =.0002).

Abemaciclib plus ET also led to an improvement in distant relapse-free survival (DRFS) compared with ET alone. The 2-year DRFS rates were 89.5% and 82.8%, respectively (HR, 0.609; 95% CI, 0.459-0.809; P =.0006).

Benefits in IDFS and DRFS were observed regardless of tumor size before or after NAC, Dr Martin noted.

The safety profile of abemaciclib plus ET in this analysis was similar to the safety profile in the overall study population.

“Our results suggest that the additional of abemaciclib to endocrine therapy results in a clinically meaningful improvement both in invasive disease-free survival and distant relapse-free survival in patients with high-risk early breast cancer that received neoadjuvant chemotherapy,” Dr. Martin said.

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.

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Martin M, Hegg R, Kim S-B, et al. Abemaciclib combined with adjuvant endocrine therapy in patients with high risk early breast cancer who received neoadjuvant chemotherapy (NAC). J Clin Oncol. 2021;39:(suppl 15; abstr 517). doi:10.1200/JCO.2021.39.15_suppl.517