Overview

A class action lawsuit has been filed against Mereo BioPharma Group plc, (“Mereo,” or the “Company”) (NASDAQ : MREO) and certain of the Company’s senior executive officers (collectively, “Defendants”) alleging violations of federal securities laws. The Mereo lawsuit is brought on behalf of all persons and entities who purchased or otherwise acquired Mereo American Depositary Shares (“ADS”) between June 5, 2023, and December 26, 2025, both dates inclusive (the “Class Period”). Investors have until April 6, 2026, to seek appointment as lead plaintiff of the Mereo class action lawsuit.

Mereo is a clinical-stage biopharmaceutical company that focuses on acquiring, developing, and advancing potential therapies for rare diseases and select specialty indications.  In July 2015, Mereo acquired the rights to setrusumab, a rare disease product candidate for the treatment of osteogenesis imperfecta (“OI”), commonly known as brittle bone disease. 

The complaint asserts that throughout the Class Period Defendants repeatedly touted positive interim and Phase 2 testing data for setrusumab, emphasizing rapid and substantial bone mineral density gains and projecting fracture‑risk reduction.  Defendants also highlighted setrusumab’s ability to achieve statistical significance for the primary endpoints in the Phase 3 ORBIT and COSMIC studies. 

The complaint alleges these statements misled shareholders regarding setrusumab’s efficacy and prospects.  In truth, Mereo oversold setrusumab’s efficacy by relying on earlier clinical data that did not support the statements being made and/or the advancement to subsequent clinical trials.  Accordingly, Defendants acted recklessly when claiming that the drug would reduce clinical fractures based on its clinically shown ability to increase bone mineral density. Furthermore, the lawsuit alleges Defendants knew or recklessly disregarded that neither ORBIT nor COSMIC would reach statistical significance against the primary endpoints of reduction in annualized clinical fracture rate compared to placebo or bisphosphonates, respectively, because the Company relied on data that failed to control for either the benefits of increased standard of care or the impact of the placebo effect.

The truth began to unravel on July 9, 2025, when Mereo disclosed that the Phase 3 ORBIT study failed to achieve statistical significance for the second interim analysis, causing the price of Mereo’s ADS to decline dramatically. On this news, Mereo’s ADS price fell $1.69 per share, a decline of approximately 42%.

The truth fully emerged on December 29, 2025, when Mereo announced that neither ORBIT nor the COSMIC Phase 3 studies achieved statistical significance. Investors and analysts reacted immediately to this information and the price of Mereo’s ADS collapsed. From a closing market price of $2.31 per share on December 26, 2025, Mereo’s ADS price fell to $0.29 per share on December 29, 2025, a decline of nearly 88%.

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If you purchased or otherwise acquired Mereo ADS between June 5, 2023, and December 26, 2025, and you wish to serve as lead plaintiff in this lawsuit, you are encouraged to submit your information to DiCello Levitt LLP via the form on this page. 

You can also contact DiCello Levitt attorneys Brian O’Mara or Hani Farah by calling (888) 287-9005 or at investors@dicellolevitt.com. 

The deadline to apply to the Court to serve as a lead plaintiff in the Mereo lawsuit is April 6, 2026.