MONARCH 2: Abemaciclib in combination with fulvestrant in Asian women with HR+, HER2- advanced breast cancer who progressed on endocrine therapy

Background: MONARCH 2 demonstrated that the addition of abemaciclib, a CDK4 & 6 inhibitor dosed on a continuous schedule, to fulvestrant (F) significantly improved progression-free survival (PFS) and objective response rate (ORR) compared to placebo (P) plus F (PFS hazard ratio [HR], 0.553, P<.0000001; ORR in measurable disease 48.1% vs 21.3%, P<.001) in women with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer who had progressed on endocrine therapy (ET). Methods: MONARCH 2 is a Phase 3 double-blind trial of abemaciclib + F vs P + F in women with HR+, HER2- advanced breast cancer. Women who progressed on (neo)adjuvant endocrine therapy (ET), ≤12 m from end of adjuvant ET, or on first line ET for MBC and who had not received chemotherapy for metastatic disease were eligible; pre/perimenopausal pts received a gonadotropin-releasing hormone agonist. Pts were randomized 2:1 to receive abemaciclib at 150 mg Q12H (or 200 mg prior to amendment) or P plus F (500 mg, per label) and stratified by metastatic site (visceral, bone only, or other) and resistance to prior ET (primary vs secondary). We present the primary objective of investigator-assessed progression-free survival (PFS), and secondary efficacy and safety endpoints in Asian pts. Results: 214 Asian pts were randomized to abemaciclib plus F (N = 149) and to P plus F (N = 65). In the ITT population, 122 PFS events were observed with a median PFS of 22.8 m for abemaciclib plus F and 11.6 m for P + F (HR: 0.515; 95% CI: 0.359, 0.740, P<.001 by log-rank test). In pts with measurable disease (n = 170, 79.4%), the ORR was significantly higher in abemaciclib plus F 48% (2.4% complete response [CR]) vs 23.4% (0% CR) for P plus F, P=.004. The most frequent adverse events for abemaciclib plus F vs P plus F were diarrhea (90.5% vs 20.0%), neutropenia (68.2% vs 4.6%), nausea (37.8% vs 16.9%), and fatigue (53.8% vs 30.9%). Conclusions: Abemaciclib + F was an effective treatment in Asian pts with HR+, HER2- advanced breast cancer who progressed on endocrine therapy with significantly improved PFS and ORR. These findings were consistent with the intent-to-treat population in MONARCH 2. Clinical trial indentification: NCT02107703. Legal entity responsible for the study: Eli Lilly and Company Funding: Eli Lilly and Company Disclosure: H. Iwata: Honoraria: Chugai Pharmaceutical, Eisai, AstraZeneca, Novartis, Daiichi Sankyo, Taiho Pharmaceutical. Research funding: GSK, Daiichi Sankyo, Chugai Pharmaceutical, Nippon Kayaku, Novartis, Pfizer, AstraZeneca, Eisai, Eli Lilly, and MSD. J.H. Sohn: Research Funding: AstraZeneca, Eli Lilly, Novartis, Genentech, Pfizer, MSD Oncology, N. Masuda: Honoraria: Chugai Pharma, AstraZeneca Research Funding: Chugai Pharma (Inst), AstraZeneca (Inst), Kyowa-Kirin (Inst), MSD Oncology (Inst), Novartis (Inst), Pfizer (Inst), Eli Lilly (Inst), Y. Lin, S. Sakaguchi, N. Bourayou: Employee of Eli Lilly and Company, A. Llombart: Honoraria: Roche, Novartis, Pfizer Consulting or Advisory Role: Roche, AstraZeneca, Eli Lilly Research Funding: Pfizer, Roche, G. Sledge: Leadership: Syndax Stock or Other Ownership: Syndax Honoraria: Symphogen Consulting or Advisory Role: Symphogen, Coherus Biosciences, Radius Health, Peregrine Pharmaceuticals, Taiho Pharmaceutical Research Funding: Roche (Inst) All other authors have declared no conflicts of interest.