Mereo BioPharma’s setrusumab misses primary endpoints in Phase 3 bone disease trials

Mereo BioPharma (NASDAQ:MREO)  said Phase 3 trials of setrusumab (UX143) in osteogenesis imperfecta failed to meet their primary endpoints, dealing a setback to the late-stage program as the company moves to cut spending and reassess priorities.

The company reported results dated Dec. 29, 2025, from the ORBIT and COSMIC studies.

Neither trial demonstrated a statistically significant reduction in annualized clinical fracture rates, the primary endpoint, compared with placebo in ORBIT or bisphosphonates in COSMIC.

Both studies did achieve their key secondary endpoints, showing statistically significant improvements in bone mineral density versus the respective comparators.

Mereo said there were no changes to the safety profile observed across the trials.

Following the results, Mereo said it will implement immediate reductions in pre-commercial and manufacturing activities related to setrusumab while conducting further analyses of the data to evaluate potential next steps.

The company also said it will continue to pursue partnering opportunities for alvelestat, another asset in its pipeline.

Mereo reported a cash balance of $48.7 million at the end of the third quarter of 2025, which management said will support operations as it refocuses resources after the Phase 3 outcome.