Class Action: Ultragenyx Pharmaceutical Sued Over Setrusumab Phase III Trial Communications

Ultragenyx Faces Suit Over Clinical Trial Communications

Allegations Focus on Setrusumab Phase III Orbit and Cosmic Studies

A securities class action filed against Ultragenyx Pharmaceutical centers on the company’s communications about its experimental bone drug setrusumab (UX-143), alleging the firm and certain executives made materially misleading statements about Phase III Orbit and Cosmic trials in osteogenesis imperfecta (OI). The complaint, filed in the U.S. District Court for the Northern District of California, says Ultragenyx publicly expressed confidence that setrusumab would reduce annualized fracture rate (AFR) and that study designs would limit variability, while allegedly failing to disclose contrary information that could undermine those claims.

Plaintiffs contend Ultragenyx’s optimism and public benchmarks rested on Phase II data that lack a placebo control, a limitation that the complaint says makes AFR reductions susceptible to influences such as improved standard of care or placebo effects rather than true drug efficacy. The suit further alleges that the company downplayed the risk that the Orbit study would fail to achieve a statistically significant reduction in AFR at a second interim analysis, a benchmark the complaint says was necessary to conduct and present that analysis as planned.

The complaint notes that on July 9, 2025 the company discloses that a second interim analysis did not achieve statistical significance and later reports that both the Phase III Orbit and Cosmic studies ultimately fail to meet their primary endpoints for reduction in annualized clinical fracture rate versus placebo. Plaintiffs argue those disclosures show earlier public statements lacked a reasonable basis and that Ultragenyx misrepresented the reliability of its information across variable OI subtypes, raising questions about trial design interpretation and the use of uncontrolled Phase II data to set Phase III expectations.

Lead Plaintiff Deadline, Multiple Notices

Several plaintiff firms — including Rosen Law, Kessler Topaz Meltzer & Check, and Robbins Geller Rudman & Dowd — are notifying investors of the pending suit and urging eligible shareholders to seek lead plaintiff status. The notices identify the class period as Aug. 3, 2023 through Dec. 26, 2025 and set an April 6, 2026 deadline to move for appointment as lead plaintiff.

The firms say investors who purchased Ultragenyx common stock during the class period may be entitled to pursue claims and may contact counsel for free case evaluations or to submit lead plaintiff applications. The litigation highlights scrutiny on how biotech companies communicate trial expectations and the risks of relying on uncontrolled early‑phase data when guiding Phase III benchmarks.