Portnoy Law Firm Announces Class Action Against Mereo BioPharma

Investors allege company misled them about failed drug trials

Feb. 26, 2026 at 4:39pm

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The Portnoy Law Firm has filed a class action lawsuit on behalf of investors who bought Mereo BioPharma Group plc (NASDAQ: MREO) securities between June 5, 2023 and December 26, 2025. The lawsuit alleges that Mereo provided overly positive statements to investors while concealing material information about the failure of its Phase 3 ORBIT and COSMIC drug trials.

Why it matters

This case highlights the importance of transparency and honesty from publicly traded companies, especially when it comes to reporting the results of critical drug trials. Investors rely on accurate information to make informed decisions, and allegations of misleading statements can erode trust in the market.

The details

According to the complaint, Mereo's ORBIT and COSMIC Phase 3 trials failed to meet their primary endpoints of reducing annualized clinical fracture rates compared to placebo or bisphosphonate control groups, despite improved bone mineral density. However, the company allegedly provided overwhelmingly positive statements to investors about the trials. On December 29, 2025, Mereo announced the trials had not achieved statistical significance, causing its stock price to plummet more than 87% in a single day.

  • The class period covers securities purchased between June 5, 2023 and December 26, 2025.
  • Mereo announced the failed trial results on December 29, 2025.

The players

Portnoy Law Firm

A law firm representing investors in pursuing claims caused by corporate wrongdoing.

Mereo BioPharma Group plc

A biopharmaceutical company that was developing drug candidates for rare diseases.

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What they’re saying

“Investors are encouraged to contact attorney Lesley F. Portnoy, by phone 844-767-8529 or email: lesley@portnoylaw.com, to discuss their legal rights, or join the case via https://portnoylaw.com/mereo-biopharma-group-plc.”

— Lesley F. Portnoy, Attorney

What’s next

Investors have until April 6, 2026 to file a lead plaintiff motion in the class action lawsuit.

The takeaway

This case highlights the need for public companies to be transparent and honest with investors, especially when it comes to reporting the results of critical drug trials. Allegations of misleading statements can severely erode investor trust and lead to significant financial losses.