TOPLINE:
Adding the cyclin-dependent kinase (CDK)-4/6 inhibitor abemaciclib to a nonsteroidal aromatase inhibitor led to a numerically longer and clinically meaningful improvement in overall survival compared with the aromatase inhibitor alone as first-line therapy in postmenopausal women with hormone receptor–positive (HR+), human epidermal growth factor receptor 2–negative (HER2−) advanced breast cancer, but overall survival outcomes failed to reach statistical significance.
METHODOLOGY:
- Close to 70% of all breast cancers are of the HR+/HER2− type. Most patients with advanced disease who receive an aromatase inhibitor will experience disease progression or recurrence in about a year.
- The MONARCH 3 study enrolled 493 postmenopausal women between November 2014 and November 2015 with HR+/HER2− advanced breast cancer who had not received prior systemic therapy in the advanced setting.
- These patients were randomly allocated to abemaciclib plus the physician's choice of either anastrozole or letrozole vs placebo plus anastrozole or letrozole.
- The primary endpoint of progression-free survival (PFS) was reported previously — median PFS of 28.2 months in the abemaciclib arm vs 14.8 months in the placebo arm (hazard ratio [HR], 0.54). In the final analysis, researchers reported overall survival outcomes at a median follow-up of 8 years.
TAKEAWAY:
- Patients who received abemaciclib had a median overall survival of 66.8 months vs 53.7 months among those in the placebo arm — a median increase of 13.1 months, which did not reach statistical significance (HR, 0.804; 95% CI, 0.637-1.015).
- For women with visceral organ metastases, median overall survival was 63.7 months with abemaciclib vs 48.8 months with placebo — a median increase of 14.9 months over placebo but also not statistically significant (HR, 0.758; 95% CI, 0.558-1.030).
- The PFS benefit reported previously in the abemaciclib arm was maintained at 8 years follow-up (median PFS of 29.0 vs 14.8 months, respectively; HR, 0.535).
- The addition of abemaciclib also delayed subsequent receipt of chemotherapy by a median of 16.1 months, and abemaciclib plus a nonsteroidal aromatase inhibitor did not lead to new safety signals.
IN PRACTICE:
The latest "data continue to support the consistent and meaningful clinical benefit abemaciclib has demonstrated across the MONARCH program," the researchers wrote. "Although the lack of statistical significance in this final [overall survival] analysis may be viewed as a limitation of these data, it is important to consider the clinical relevance of the absolute effect size," the authors added.
SOURCE:
The study, with first author Matthew P. Goetz, MD, Department of Oncology, Mayo Clinic, Rochester, Minnesota, was published online last month in Annals of Oncology.
LIMITATIONS:
The patient population in MONARCH 3 was smaller than that in other pivotal trials of CDK4/6 inhibitors in the first-line advanced breast cancer setting, which may help explain why the overall survival endpoint did not reach statistical significance.
DISCLOSURES:
The study was funded by Eli Lilly. Goetz and other authors reported various relationships with industry, including Eli Lilly, Novartis, Roche, Pfizer, and AstraZeneca. A complete list of author disclosures is available with the paper.