Positive results from MONARCH -1 trial of abemaciclib in patients with hormone-receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer.-Eli Lilly

Eli Lilly and Company announced results from the MONARCH 1 Phase II study of abemaciclib, a cyclin-dependent kinase (CDK) 4 and CDK 6 inhibitor, in patients with hormone-receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer. The data, which were presented at the 2016 American Society of Clinical Oncology (ASCO) Annual Meeting by Maura Dickler, M.D., of Memorial Sloan Kettering Cancer Center, showed that single-agent activity was observed in metastatic breast cancer patients, for whom endocrine therapy was no longer a suitable treatment option. The MONARCH 1 results (abstract #510) confirmed objective response (ORR), durability of response (DoR), clinical benefit rate (CBR) and progression-free survival (PFS).

The single-arm study, designed to evaluate the safety and efficacy of abemaciclib monotherapy, enrolled 132 patients who were given 200 mg of abemaciclib orally every 12 hours until disease progression. Patients enrolled in the study were heavily pretreated, having experienced progressive disease on or after prior endocrine therapy, and had received prior chemotherapy with one or two chemotherapy regimens for metastatic disease. The primary objective of the trial was investigator-assessed ORR (objective response), with secondary endpoints of DoR (durability of response ), CBR (clinical benefit rate) and PFS (progression-free survival). At the final analysis of response (minimum of 12 months follow-up), patients treated with abemaciclib achieved an ORR of 19.7 percent (95% confidence interval (CI): 13.3 - 27.5%), with a median time to response of 3.7 months and a median DoR of 8.6 months. The median PFS was six months with a CBR (defined as patients who achieved complete response, partial response or stable disease for six months or longer) of 42.4 percent. Of the 13 patients who remained on treatment at the time of this analysis, nine were responders and four had stable disease (SD).

The safety and toxicity profile of twice daily, continuously dosed abemaciclib was consistent with previous Phase 1 experience. The most common grade 3 non-laboratory treatment emergent adverse events (AEs) were diarrhea (19.7%) and fatigue (12.9%), with no grade 4 non-laboratory events reported. The most common laboratory AEs were neutropenia (22.3% grade 3, 4.6% grade 4) and leukopenia (27.4% grade 3) in this population; 7.6 percent of patients discontinued treatment due to AEs, one due to diarrhea.

Comment: Abemaciclib is being evaluated in two Phase III clinical trials: MONARCH 2 to evaluate the combination of abemaciclib and fulvestrant for treatment of HR+, HER2- advanced or metastatic breast cancer in postmenopausal women, and MONARCH 3 to evaluate the combination of abemaciclib and a nonsteroidal aromatase inhibitor in HR+, HER2- locoregionally recurrent or metastatic breast cancer in postmenopausal women.