Mereo BioPharma Shares Plunge 87.5% After Phase 3 Study Fails to Meet Primary Endpoints
Written by Emily J. Thompson, Senior Investment Analyst
Updated: Dec 29 2025
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Should l Buy MREO?
Source: Benzinga
- Study Failure: Mereo BioPharma's Phase 3 ORBIT and COSMIC studies failed to achieve statistical significance in reducing clinical fracture rates, causing shares to plummet 87.5% to $0.29 in pre-market trading, severely undermining market confidence in the company.
- Partner Impact: Ultragenyx Pharmaceutical, a partner of Mereo, also saw its shares drop 43.7% to $19.26, reflecting investor pessimism about the drug's prospects, which may affect future collaborations and funding for research and development.
- Market Reaction: Other related stocks, such as SPAC III Acquisition Corp and Sellas Life Sciences, experienced declines of 11.7% and 7.6%, respectively, indicating a broader erosion of confidence in the biotech sector among investors.
- Investor Sentiment: The failure of Mereo's studies has dampened investor sentiment in the biotech field, potentially leading to capital outflows and stricter financing conditions that could hinder the growth of other companies in the industry.
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Analyst Views on MREO
Wall Street analysts forecast MREO stock price to rise
8 Analyst Rating
6 Buy
2 Hold
0 Sell
Strong Buy
Current: 0.416
Low
0.50
Averages
2.08
High
5.00
Current: 0.416
Low
0.50
Averages
2.08
High
5.00
About MREO
Mereo BioPharma Group plc is a biopharmaceutical company focused on the development of therapeutics for rare diseases. The Company has developed a portfolio of late-stage clinical product candidates, and its two rare disease product candidates are setrusumab for the treatment of osteogenesis imperfecta (OI) and alvelestat primarily for the treatment of severe alpha-1 antitrypsin deficiency-associated lung disease (AATD-LD). In addition to the rare disease programs, it has two oncology product candidates in clinical development, which include Etigilimab, an IgG1 monoclonal antibody which binds to the human T-cell immunoreceptor with Ig and ITIM domains (TIGIT) receptor on immune cells to improve the activation and effectiveness of T-cell and NK cell antitumor activity and Navicixizumab is a bispecific antibody that inhibits delta-like ligand 4 (DLL4) and vascular endothelial growth factor (VEGF). Navicixizumab is developed for the treatment of late-line ovarian cancer.
About the author
Emily J. Thompson
Emily J. Thompson, a Chartered Financial Analyst (CFA) with 12 years in investment research, graduated with honors from the Wharton School. Specializing in industrial and technology stocks, she provides in-depth analysis for Intellectia’s earnings and market brief reports.
Mereo BioPharma Shareholder Notice Issued
- Lawsuit Notice Issued: The Gross Law Firm has issued a notice to shareholders of Mereo BioPharma Group plc, encouraging those who purchased shares during the class period from June 5, 2023, to December 26, 2025, to contact the firm regarding potential lead plaintiff appointment for recovery participation.
- False Statement Allegations: The complaint alleges that Mereo BioPharma made overwhelmingly positive statements about its Phase 3 ORBIT and COSMIC programs while concealing significant adverse facts regarding the clinical fracture rate, misleading investors about the company's performance.
- Clinical Trial Failures: On December 29, 2025, Mereo announced that neither the ORBIT nor COSMIC studies achieved statistical significance in reducing clinical fracture rates, despite improvements in bone mineral density, leading to a dramatic decline in stock price following the announcement.
- Stock Price Collapse: Following the announcement, Mereo's ADS price plummeted from $2.31 per share on December 26, 2025, to $0.29 per share on December 29, 2025, representing a staggering decline of over 87.7%, severely impacting shareholder value.
See More
Class Action Reminder for Mereo BioPharma Shareholders
- Lawsuit Background: Robbins LLP reminds all investors who purchased Mereo BioPharma Group plc (NASDAQ: MREO) American Depository Shares between June 5, 2023, and December 26, 2025, that a class action has been filed, alleging the company misled investors regarding clinical trial results.
- Study Failures: The complaint indicates that Mereo failed to meet the primary endpoint of reducing clinical fracture rates in its Phase 3 ORBIT and COSMIC studies, despite previously optimistic statements about the drug setrusumab, leading investors to buy shares at artificially inflated prices.
- Stock Price Plunge: Following the announcement on December 29, 2025, that the studies did not meet their endpoints, Mereo's ADS price plummeted from $2.31 on December 26, 2025, to $0.29, representing a decline of over 87.7%, severely impacting shareholder value.
- Next Steps: Shareholders wishing to serve as lead plaintiffs in the class action must submit their papers by April 6, 2026; Robbins LLP offers contingency fee representation, ensuring shareholders can recover losses without upfront costs.
See More
Mereo BioPharma Faces Class Action Lawsuit
- Class Action Initiated: Berger Montague PC has filed a class action lawsuit against Mereo BioPharma on behalf of investors who purchased American Depositary Shares between June 5, 2023, and December 26, 2025, indicating significant investor disappointment regarding the company's outlook.
- Stock Price Plunge: Following Mereo's disclosure on December 29, 2025, that its ORBIT and COSMIC Phase 3 trials failed to meet primary endpoints, the ADS price plummeted over 87% from $2.31 on December 26, 2025, to $0.29, reflecting market pessimism about the company's future.
- Investor Rights: Investors must apply by April 6, 2026, to be appointed as lead plaintiffs in the class action, highlighting the urgency of the legal action and its potential impact on investors.
- Company Background: Mereo is a biopharmaceutical company focused on developing therapies for rare and serious diseases, headquartered in London, UK, and the legal challenges it faces may affect its future financing and R&D capabilities.
See More
Ultragenyx and Mereo Face Class Action Lawsuits
- Lawsuit Background: Bragar Eagel & Squire, P.C. has alerted investors that Ultragenyx Pharmaceutical Inc. and Mereo BioPharma Group plc are facing class action lawsuits, with a deadline of April 6, 2026, for investors to apply as lead plaintiffs, indicating significant investor concern over potential risks associated with these companies.
- Ultragenyx Lawsuit Details: On December 29, 2025, Ultragenyx announced that its Phase III Orbit and Cosmic studies failed to achieve statistical significance in reducing fracture rates, causing its stock price to plummet from $34.19 to $19.72, a decline of 42.32%, reflecting market disappointment in the study results.
- Mereo Lawsuit Details: Mereo BioPharma faces similar allegations as its Phase 3 ORBIT and COSMIC studies did not meet the primary endpoint of reducing annualized fracture rates, leading to a drastic drop in its stock price from $2.31 to $0.29, a decline of over 87.7%, showcasing extreme investor pessimism regarding its prospects.
- Investor Impact: Both companies are accused of failing to disclose research risks adequately, resulting in shareholders purchasing stocks at inflated prices; the initiation of class action lawsuits may severely impact their future financing and market confidence, exacerbating investor anxiety.
See More
Class Action Lawsuit Filed Against Mereo BioPharma Group plc
- Class Action Initiation: Pomerantz LLP has announced a class action lawsuit against Mereo BioPharma, alleging securities fraud by the company and certain executives, with investors advised to apply as Lead Plaintiff by April 6, 2026, indicating significant legal risks that could impact stock price and market confidence.
- Stock Price Plunge: On December 29, 2025, Mereo disclosed that neither the Orbit nor Cosmic Phase 3 studies achieved statistical significance, resulting in an 87.7% drop in its American Depositary Receipt (ADR) price to $0.29, reflecting extreme investor pessimism regarding the company's future prospects.
- Poor Research Outcomes: Although Mereo and its partner Ultragenyx reported progress in July 2025, the final analysis revealed failure to meet primary endpoints, indicating major setbacks in critical R&D projects that could affect future financing and partnership opportunities.
- Law Firm Background: Pomerantz LLP, a leading firm in securities class litigation with over 85 years of experience, focuses on the rights of victims of securities fraud and corporate misconduct, highlighting the potential impact and complexity of this case, which may attract further investor attention.
See More
Class Action Filed Against Mereo BioPharma Group plc for Securities Violations
- Class Action Initiated: Bronstein, Gewirtz & Grossman, LLC has announced a class action lawsuit against Mereo BioPharma Group plc, aiming to recover damages for investors who purchased securities between June 5, 2023, and December 26, 2025, reflecting strong investor concerns over potential fraud.
- Allegations of False Statements: The complaint alleges that throughout the class period, defendants made overly positive statements while concealing significant adverse facts regarding the Phase 3 ORBIT and COSMIC programs, leading to investor misconceptions about the company's true condition, which could impact stock prices.
- Investor Action Deadline: Affected investors have until April 6, 2026, to request appointment as lead plaintiff to share in any potential recovery, highlighting the legal system's role in protecting investor rights.
- No-Cost Legal Representation: Bronstein, Gewirtz & Grossman, LLC offers contingency fee-based legal services, charging only if successful in claims, ensuring that investors can pursue justice without incurring additional financial burdens.
See More
Mereo BioPharma Shareholder Notice Issued
- Lawsuit Notice Issued: The Gross Law Firm has issued a notice to shareholders of Mereo BioPharma Group plc, encouraging those who purchased shares during the class period from June 5, 2023, to December 26, 2025, to contact the firm regarding potential lead plaintiff appointment for recovery participation.
- False Statement Allegations: The complaint alleges that Mereo BioPharma made overwhelmingly positive statements about its Phase 3 ORBIT and COSMIC programs while concealing significant adverse facts regarding the clinical fracture rate, misleading investors about the company's performance.
- Clinical Trial Failures: On December 29, 2025, Mereo announced that neither the ORBIT nor COSMIC studies achieved statistical significance in reducing clinical fracture rates, despite improvements in bone mineral density, leading to a dramatic decline in stock price following the announcement.
- Stock Price Collapse: Following the announcement, Mereo's ADS price plummeted from $2.31 per share on December 26, 2025, to $0.29 per share on December 29, 2025, representing a staggering decline of over 87.7%, severely impacting shareholder value.
See More
Class Action Reminder for Mereo BioPharma Shareholders
- Lawsuit Background: Robbins LLP reminds all investors who purchased Mereo BioPharma Group plc (NASDAQ: MREO) American Depository Shares between June 5, 2023, and December 26, 2025, that a class action has been filed, alleging the company misled investors regarding clinical trial results.
- Study Failures: The complaint indicates that Mereo failed to meet the primary endpoint of reducing clinical fracture rates in its Phase 3 ORBIT and COSMIC studies, despite previously optimistic statements about the drug setrusumab, leading investors to buy shares at artificially inflated prices.
- Stock Price Plunge: Following the announcement on December 29, 2025, that the studies did not meet their endpoints, Mereo's ADS price plummeted from $2.31 on December 26, 2025, to $0.29, representing a decline of over 87.7%, severely impacting shareholder value.
- Next Steps: Shareholders wishing to serve as lead plaintiffs in the class action must submit their papers by April 6, 2026; Robbins LLP offers contingency fee representation, ensuring shareholders can recover losses without upfront costs.
See More
Mereo BioPharma Faces Class Action Lawsuit
- Class Action Initiated: Berger Montague PC has filed a class action lawsuit against Mereo BioPharma on behalf of investors who purchased American Depositary Shares between June 5, 2023, and December 26, 2025, indicating significant investor disappointment regarding the company's outlook.
- Stock Price Plunge: Following Mereo's disclosure on December 29, 2025, that its ORBIT and COSMIC Phase 3 trials failed to meet primary endpoints, the ADS price plummeted over 87% from $2.31 on December 26, 2025, to $0.29, reflecting market pessimism about the company's future.
- Investor Rights: Investors must apply by April 6, 2026, to be appointed as lead plaintiffs in the class action, highlighting the urgency of the legal action and its potential impact on investors.
- Company Background: Mereo is a biopharmaceutical company focused on developing therapies for rare and serious diseases, headquartered in London, UK, and the legal challenges it faces may affect its future financing and R&D capabilities.
See More
Ultragenyx and Mereo Face Class Action Lawsuits
- Lawsuit Background: Bragar Eagel & Squire, P.C. has alerted investors that Ultragenyx Pharmaceutical Inc. and Mereo BioPharma Group plc are facing class action lawsuits, with a deadline of April 6, 2026, for investors to apply as lead plaintiffs, indicating significant investor concern over potential risks associated with these companies.
- Ultragenyx Lawsuit Details: On December 29, 2025, Ultragenyx announced that its Phase III Orbit and Cosmic studies failed to achieve statistical significance in reducing fracture rates, causing its stock price to plummet from $34.19 to $19.72, a decline of 42.32%, reflecting market disappointment in the study results.
- Mereo Lawsuit Details: Mereo BioPharma faces similar allegations as its Phase 3 ORBIT and COSMIC studies did not meet the primary endpoint of reducing annualized fracture rates, leading to a drastic drop in its stock price from $2.31 to $0.29, a decline of over 87.7%, showcasing extreme investor pessimism regarding its prospects.
- Investor Impact: Both companies are accused of failing to disclose research risks adequately, resulting in shareholders purchasing stocks at inflated prices; the initiation of class action lawsuits may severely impact their future financing and market confidence, exacerbating investor anxiety.
See More
Class Action Lawsuit Filed Against Mereo BioPharma Group plc
- Class Action Initiation: Pomerantz LLP has announced a class action lawsuit against Mereo BioPharma, alleging securities fraud by the company and certain executives, with investors advised to apply as Lead Plaintiff by April 6, 2026, indicating significant legal risks that could impact stock price and market confidence.
- Stock Price Plunge: On December 29, 2025, Mereo disclosed that neither the Orbit nor Cosmic Phase 3 studies achieved statistical significance, resulting in an 87.7% drop in its American Depositary Receipt (ADR) price to $0.29, reflecting extreme investor pessimism regarding the company's future prospects.
- Poor Research Outcomes: Although Mereo and its partner Ultragenyx reported progress in July 2025, the final analysis revealed failure to meet primary endpoints, indicating major setbacks in critical R&D projects that could affect future financing and partnership opportunities.
- Law Firm Background: Pomerantz LLP, a leading firm in securities class litigation with over 85 years of experience, focuses on the rights of victims of securities fraud and corporate misconduct, highlighting the potential impact and complexity of this case, which may attract further investor attention.
See More
Class Action Filed Against Mereo BioPharma Group plc for Securities Violations
- Class Action Initiated: Bronstein, Gewirtz & Grossman, LLC has announced a class action lawsuit against Mereo BioPharma Group plc, aiming to recover damages for investors who purchased securities between June 5, 2023, and December 26, 2025, reflecting strong investor concerns over potential fraud.
- Allegations of False Statements: The complaint alleges that throughout the class period, defendants made overly positive statements while concealing significant adverse facts regarding the Phase 3 ORBIT and COSMIC programs, leading to investor misconceptions about the company's true condition, which could impact stock prices.
- Investor Action Deadline: Affected investors have until April 6, 2026, to request appointment as lead plaintiff to share in any potential recovery, highlighting the legal system's role in protecting investor rights.
- No-Cost Legal Representation: Bronstein, Gewirtz & Grossman, LLC offers contingency fee-based legal services, charging only if successful in claims, ensuring that investors can pursue justice without incurring additional financial burdens.
See More
