Initial Ribociclib Plus Endocrine Therapy for HR+/HER2-advanced Breast Cancer in Pre- and Postmenopausal Chinese Women: Primary Results from a Phase 2 Randomized Study

Background: The MONALEESA-7 and -2 phase 3 randomized trials demonstrated a statistically significant progression-free survival (PFS) and overall survival (OS) benefit with initial ribociclib + endocrine therapy (ET) versus placebo + ET in pre- and postmenopausal patients with hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC), respectively. Similar trends were observed in Asian subgroup analyses. This phase 2 bridging study of initial ET + ribociclib enrolled pre- and postmenopausal patients with HR+/HER2- ABC from China and was conducted to demonstrate consistency of PFS results in a Chinese population relative to the global MONALEESA-7 and -2 studies. Methods: Patients were randomized (1:1) to ET (nonsteroidal aromatase inhibitor + goserelin for premenopausal patients; letrozole for postmenopausal patients) + either ribociclib or placebo. The primary endpoint was investigator-assessed PFS. Results: As of April 25, 2022, the median follow-up was 34.7 months in both cohorts. In the premenopausal cohort, median PFS was 27.6 months in the ribociclib arm (n = 79) versus 14.7 months in the placebo arm (n = 77) (hazard ratio 0.67 [95% CI: 0.45, 1.01]). In the postmenopausal cohort, median PFS was not reached in the ribociclib arm versus 18.5 months in the placebo arm (n = 77 in each arm) (hazard ratio 0.40 [95% CI: 0.26, 0.62]). Data also suggested improvements in secondary efficacy endpoints, although OS data were not mature. The safety profile in this population was consistent with that in global studies. Conclusions: These data demonstrate a favorable benefit-risk profile for ribociclib + ET in Chinese patients.