Two late-stage Phase III readouts for setrusumab failed to meet primary endpoints, prompting immediate program and market fallout. Ultragenyx Pharmaceutical Inc. and Mereo BioPharma Group plc disclosed the negative results from the Orbit and Cosmic trials; both companies reported secondary endpoint activity but not the prespecified primary outcomes. The readouts triggered heavy selling: Mereo shares plunged precipitously at the open and Ultragenyx shares fell sharply, reflecting investor reassessment of the program’s commercial potential. Both companies said they are reviewing the data to determine next steps for the asset and any implications for broader R&D plans. Clinicians and investors will watch follow-up analyses for subgroup signals and safety details; regulators and potential partners typically reassess late-stage failures for rescue strategies but such moves are uncommon when primary endpoints are missed. The failures further underscore the sector risk when single-asset biotechs hinge on one pivotal program.