MONARCH 3: Updated time to chemotherapy and disease progression following abemaciclib plus aromatase inhibitor (AI) in HR+, HER2- advanced breast cancer (ABC)

Abstract

Background: In MONARCH 3, a randomized, double-blind, phase 3 trial; continuous dosing of abemaciclib in combination with an AI (anastrozole or letrozole) conferred significant clinical benefit to postmenopausal women with HR+, HER2-ABC. We here report data from an additional 12 months of follow-up in this trial including analysis for clinically prognostic subgroups (Di Leo et al., 2018). Method(s): From the 31 October 2018 data cutoff, exploratory intermediate efficacy parameters including time to subsequent chemotherapy ([TCT] time from randomization to first chemotherapy [CT]) and time to second disease progression ([PFS2] time from randomization to discontinuation date of first post-discontinuation treatment [PDT], or starting date of the secondPDT, or death) were assessed. TCT and PFS2 were analyzed using the Kaplan-Meier method in the intent to treat (ITT) and subgroups previously identified as significantly prognostic. Result(s): In the ITT population, updated PFS was 28.2 vs 14.8 months (HR [95% CI]: 0.525 [0.415, 0.665]; p