Ultragenyx Pharmaceutical Inc. (RARE) shares fell sharply, trading at $18.93, down $15.26 or 44.63%, after the company reported mixed results from its Phase 3 ORBIT and COSMIC studies of setrusumab (UX143) for osteogenesis imperfecta.
The company said neither study achieved its primary goal of significantly reducing annualised clinical fracture rates compared to placebo or standard treatment, disappointing investors and triggering a selloff. Both trials did show statistically significant improvements in bone mineral density, a secondary endpoint, and no new safety concerns were observed.
In the ORBIT study, improvements in bone density did not correspond with lower fracture rates, in part due to a low fracture incidence in the control group. In the pediatric COSMIC trial, while bone mineral density gains were linked with lower fracture rates compared to bisphosphonate therapy, those results did not reach statistical significance.
Ultragenyx said it will conduct deeper analyses of the data and evaluate next steps for the setrusumab programme, including exploring additional bone health and clinical endpoints. The company also announced plans for significant expense reductions as it reassesses operational priorities following the setback.
RARE's 52-week range reflects substantial volatility, driven by clinical readouts and development progress in its rare disease pipeline. Investors will likely watch for further updates on data interpretation, potential regulatory strategy changes, and the company's broader pipeline execution.
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