Two Phase III programs of setrusumab failed to meet primary endpoints, prompting Ultragenyx Pharmaceutical and Mereo BioPharma to suspend plans and triggering dramatic market reactions. The late‑stage readouts left both developers re‑evaluating their clinical strategies and left investors reassessing the risk profile for similar bone‑disease programs. Market response was swift: Mereo shares plunged to multiyear lows and Ultragenyx also saw heavy selling. The outcomes underscore the binary risk inherent in late‑stage rare disease trials and may influence partner interest, financing availability and timelines for other companies developing biologics in bone fragility indications.