Abemaciclib plus Fulvestrant Provides Statistically Significant Benefit as First- and Second-Line Therapy for Hormone Receptor–Positive, HER2-Negative Advanced Breast Cancer

In addition to the significant benefit observed in the MONARCH 2 study across first- and second-line treatment, marked effects were observed in patients with less encouraging prognostic indicators.

In the MONARCH 2 study, abemaciclib, an oral selective CDK4/6 inhibitor, plus fulvestrant demonstrated statistically significant improvements in progression-free survival (PFS) and overall survival (OS) compared with placebo plus fulvestrant in hormone receptor–positive, HER2-negative advanced breast cancer. Numerically more pronounced improvement in PFS and OS was noted in subgroups with visceral disease and primary endocrine resistance.

Patrick Neven, MD, PhD, Oncologist, Gynecologic Oncology, University Hospital Leuven, Belgium, and colleagues reported PFS and OS for MONARCH 2 with respect to first- and second-line treatment outcomes.

This was an international, randomized, double-blind phase 3 trial of abemaciclib and fulvestrant (N = 446) or placebo and fulvestrant (N = 223) in women with endocrine therapy–resistant, hormone receptor–positive, HER2-negative advanced breast cancer regardless of menopausal status. Stratification of patients was conducted by resistance to previous endocrine therapy (primary vs secondary) and site of metastasis (visceral, bone-only, or other).

In 2019, at the time of data cutoff, the effect of abemaciclib and fulvestrant compared with placebo and fulvestrant was consistent across first-line therapy and second-line therapy. The subanalysis revealed no statistically significant impact on PFS (P = .341) or OS (P = .265). For patients receiving it as first-line therapy, improvement in PFS was demonstrated (hazard ratio [HR], 0.57; 95% confidence interval [CI], 0.45-0.73); within this population, there was also a positive impact on OS (HR, 0.85; 95% CI, 0.64-1.14). In the second-line therapy setting, efficacy was similar as shown in data from PFS (HR, 0.48; 95% CI, 0.36-0.64) as well as OS (HR, 0.66; 95% CI, 0.46-0.94).

The most profound effects were shown in the first-line therapy population in which patients had less favorable prognostic indicators, such as primary endocrine therapy resistance (PFS: HR, 0.40; 95% CI, 0.26-0.63; OS: HR, 0.58; 95% CI, 0.35-0.97) and visceral disease (PFS: HR, 0.54; 95% CI, 0.39-0.73; OS: HR, 0.82; 95% CI, 0.57-1.17).

The investigators concluded that, in the MONARCH 2 study, the observed statistically significant benefit was across first- and second-line therapy patients. In patients treated with abemaciclib and fulvestrant in the first-line therapy setting, improvements were observed for PFS and OS with profound effects noted in patients with resistance to primary endocrine therapy and visceral disease.

Source: Neven P, Johnston SRD, Toi M, et al. MONARCH 2: subgroup analysis of patients receiving abemaciclib + fulvestrant as first- and second-line therapy for HR+, HER2- advanced breast cancer. J Clin Oncol. 2020;38(15_suppl). Abstract 1061.

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