Mereo BioPharma Group plc 8-K

What Happened

• On December 29, 2025 Mereo BioPharma Group plc announced results from its Phase 3 ORBIT and COSMIC studies of setrusumab (UX143) in pediatric and young adult patients with osteogenesis imperfecta (OI). Neither trial achieved statistical significance on the primary endpoint (reduction in annualized clinical fracture rate vs. placebo in ORBIT and vs. bisphosphonates in COSMIC). Both studies did, however, meet secondary endpoints demonstrating statistically significant improvements in bone mineral density (BMD) versus their comparators. The company reported no change in the safety profile.

Key Details

• Date filed: Form 8-K dated December 29, 2025; press release attached as Exhibit 99.1.
• Primary endpoints: Neither ORBIT nor COSMIC achieved statistical significance for reduction in annualized clinical fracture rate (vs. placebo and vs. bisphosphonates, respectively).
• Secondary endpoints: Both studies showed strong, statistically significant improvements in BMD consistent with Phase 2 results (ORBIT) and associated with fracture-rate reductions in COSMIC (not statistically significant).
• Safety: No new safety signals; overall safety profile unchanged. Additional analyses across both studies and other clinical/bone-health endpoints are ongoing.

Why It Matters

• For investors, failing to meet the primary fracture endpoint is a materially important outcome for Mereo’s setrusumab program because primary endpoint results typically drive regulatory and commercial prospects. The robust BMD improvements and unchanged safety profile may support further analysis, potential discussions with regulators or partners, or alternative development strategies, but the company has not presented new regulatory plans in this filing. Mereo also included standard forward‑looking statement cautions that further developments, analyses and risks could affect future results.