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
0mins
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: 0.392
Low
0.50
Averages
2.08
High
5.00
Current: 0.392
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.
Reminder of Class Action for Mereo BioPharma ADS Purchasers
- Class Action Notice: Rosen Law Firm reminds investors who purchased Mereo BioPharma ADS between June 5, 2023, and December 26, 2025, to apply as lead plaintiffs by April 6, 2026, to participate in the class action and potentially receive compensation.
- Lawsuit Background: The lawsuit alleges that defendants provided misleading information regarding the expected results of the Phase 3 Orbit and COSMIC studies for setrusumab, leading investors to purchase ADS at artificially inflated prices, resulting in financial losses when the truth emerged.
- Law Firm Credentials: Rosen Law Firm specializes in securities class actions and has recovered over $438 million for investors in 2019 alone, being ranked first in 2017 for the number of securities class action settlements, demonstrating its expertise and success in this field.
- Investor Guidance: Investors are advised to select counsel with a proven track record to ensure effective legal support in the class action, avoiding firms that merely act as intermediaries without substantial litigation experience.
See More
Reminder of Class Action for Mereo BioPharma ADS Purchasers
- Class Action Notice: Rosen Law Firm reminds investors who purchased Mereo BioPharma ADS between June 5, 2023, and December 26, 2025, to apply to be lead plaintiff by April 6, 2026, to potentially receive compensation without any out-of-pocket costs.
- Case Background: The lawsuit alleges that defendants provided false and misleading information regarding the Phase 3 Orbit and COSMIC studies, claiming setrusumab could significantly reduce annual fracture rates in Osteogenesis Imperfecta patients, while the studies failed to meet primary endpoints, leading investors to purchase ADS at inflated prices.
- Law Firm Credentials: Rosen Law Firm specializes in securities class actions and has achieved the largest settlement against a Chinese company, recovering over $438 million for investors in 2019 alone, demonstrating its strong track record and expertise in this field.
- Investor Advisory: Investors are advised to choose legal counsel carefully, as Rosen Law Firm emphasizes the importance of selecting experienced attorneys to ensure effective legal representation in class actions.
See More
Class Action Notice for Mereo BioPharma Investors
- Class Action Notice: The Portnoy Law Firm advises Mereo BioPharma Group plc investors of a class action for those who purchased securities between June 5, 2023, and December 26, 2025, with a deadline of April 6, 2026, to file a lead plaintiff motion to protect their legal rights.
- False Statements Allegations: The complaint alleges that defendants provided overly positive statements while concealing significant adverse facts regarding the true status of the Phase 3 ORBIT and COSMIC programs, misleading investors about the company's actual condition.
- Clinical Trial Failures: On December 29, 2025, Mereo announced that neither the ORBIT nor COSMIC Phase 3 studies achieved statistical significance, failing to meet their primary endpoint of reducing annualized clinical fracture rates compared to placebo or bisphosphonates, despite improvements in bone mineral density.
- Stock Price Collapse: Following this 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 dramatic decline of over 87.7%, severely impacting investor asset values.
See More
Ultragenyx and Mereo BioPharma Class Action Reminder
- Lawsuit Initiation: Bragar Eagel & Squire law firm has commenced class actions on behalf of shareholders of Ultragenyx Pharmaceutical (NASDAQ:RARE) and Mereo BioPharma (NASDAQ:MREO), with a lead plaintiff deadline of April 6, 2026, indicating significant investor concern regarding potential risks associated with these companies.
- Study Result Failures: On December 29, 2025, Ultragenyx announced that its Phase III Orbit and Cosmic studies failed to achieve statistical significance in reducing annualized fracture rates, causing its stock price to plummet by approximately 42.32% in a single day, from $34.19 to $19.72, reflecting market disappointment in the study outcomes.
- Mereo BioPharma's Reaction: Similarly, Mereo BioPharma announced on December 29, 2025, that its ORBIT and COSMIC studies did not meet the primary endpoint of reducing annualized clinical fracture rates, despite improved bone mineral density, leading to a dramatic decline in its ADS price from $2.31 to $0.29, a drop of over 87.7%, highlighting severe investor confidence erosion.
- Disclosure Issues: The lawsuits allege that both companies provided overly optimistic projections to investors while concealing significant adverse facts related to the study protocols, resulting in shareholders purchasing stocks at artificially inflated prices, raising concerns about corporate governance and transparency.
See More
Class Action Notice for Mereo BioPharma Investors
- Class Action Deadline: Investors in Mereo BioPharma Group plc must apply to be lead plaintiffs by April 6, 2026, to potentially receive compensation without any out-of-pocket costs, indicating a significant impact on investor confidence regarding the company's future.
- False Statements Allegations: The lawsuit alleges that the company misrepresented the expected outcomes of the Phase 3 Orbit and COSMIC studies for setrusumab, leading investors to purchase ADS at inflated prices, highlighting serious deficiencies in the company's transparency and information disclosure practices.
- Law Firm Credentials: The Rosen Law Firm specializes in securities class actions and has recovered over $438 million for investors in 2019 alone, showcasing its proven track record and expertise in handling similar cases, which enhances investor trust in their representation.
- Investor Guidance: The law firm advises investors to select qualified counsel with a successful track record to avoid partnering with inexperienced intermediaries, ensuring they receive the best legal support and potential compensation in the class action.
See More
Class Action Filed Against Mereo BioPharma Group for Securities Violations
- Class Action Initiated: Bronstein, Gewirtz & Grossman LLC has filed a class action lawsuit against Mereo BioPharma Group, seeking damages for investors who purchased securities between June 5, 2023, and December 26, 2025, reflecting strong investor response to potential fraud allegations.
- Allegations of False Statements: The complaint alleges that Mereo provided overly positive statements to investors while concealing significant adverse facts regarding the Phase 3 ORBIT and COSMIC programs, which failed to meet their primary endpoints, potentially undermining investor confidence.
- Call to Action for Investors: Affected investors are encouraged to apply to be lead plaintiffs by April 6, 2026, to share in any potential recovery from the lawsuit, indicating the legal team's commitment to protecting investor rights.
- No-Cost Legal Services: The law firm offers legal representation on a contingency fee basis, meaning they will only charge fees if they successfully recover funds, thereby reducing the legal risk for investors and enhancing the appeal of participating in the lawsuit.
See More
Reminder of Class Action for Mereo BioPharma ADS Purchasers
- Class Action Notice: Rosen Law Firm reminds investors who purchased Mereo BioPharma ADS between June 5, 2023, and December 26, 2025, to apply as lead plaintiffs by April 6, 2026, to participate in the class action and potentially receive compensation.
- Lawsuit Background: The lawsuit alleges that defendants provided misleading information regarding the expected results of the Phase 3 Orbit and COSMIC studies for setrusumab, leading investors to purchase ADS at artificially inflated prices, resulting in financial losses when the truth emerged.
- Law Firm Credentials: Rosen Law Firm specializes in securities class actions and has recovered over $438 million for investors in 2019 alone, being ranked first in 2017 for the number of securities class action settlements, demonstrating its expertise and success in this field.
- Investor Guidance: Investors are advised to select counsel with a proven track record to ensure effective legal support in the class action, avoiding firms that merely act as intermediaries without substantial litigation experience.
See More
Reminder of Class Action for Mereo BioPharma ADS Purchasers
- Class Action Notice: Rosen Law Firm reminds investors who purchased Mereo BioPharma ADS between June 5, 2023, and December 26, 2025, to apply to be lead plaintiff by April 6, 2026, to potentially receive compensation without any out-of-pocket costs.
- Case Background: The lawsuit alleges that defendants provided false and misleading information regarding the Phase 3 Orbit and COSMIC studies, claiming setrusumab could significantly reduce annual fracture rates in Osteogenesis Imperfecta patients, while the studies failed to meet primary endpoints, leading investors to purchase ADS at inflated prices.
- Law Firm Credentials: Rosen Law Firm specializes in securities class actions and has achieved the largest settlement against a Chinese company, recovering over $438 million for investors in 2019 alone, demonstrating its strong track record and expertise in this field.
- Investor Advisory: Investors are advised to choose legal counsel carefully, as Rosen Law Firm emphasizes the importance of selecting experienced attorneys to ensure effective legal representation in class actions.
See More
Class Action Notice for Mereo BioPharma Investors
- Class Action Notice: The Portnoy Law Firm advises Mereo BioPharma Group plc investors of a class action for those who purchased securities between June 5, 2023, and December 26, 2025, with a deadline of April 6, 2026, to file a lead plaintiff motion to protect their legal rights.
- False Statements Allegations: The complaint alleges that defendants provided overly positive statements while concealing significant adverse facts regarding the true status of the Phase 3 ORBIT and COSMIC programs, misleading investors about the company's actual condition.
- Clinical Trial Failures: On December 29, 2025, Mereo announced that neither the ORBIT nor COSMIC Phase 3 studies achieved statistical significance, failing to meet their primary endpoint of reducing annualized clinical fracture rates compared to placebo or bisphosphonates, despite improvements in bone mineral density.
- Stock Price Collapse: Following this 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 dramatic decline of over 87.7%, severely impacting investor asset values.
See More
Ultragenyx and Mereo BioPharma Class Action Reminder
- Lawsuit Initiation: Bragar Eagel & Squire law firm has commenced class actions on behalf of shareholders of Ultragenyx Pharmaceutical (NASDAQ:RARE) and Mereo BioPharma (NASDAQ:MREO), with a lead plaintiff deadline of April 6, 2026, indicating significant investor concern regarding potential risks associated with these companies.
- Study Result Failures: On December 29, 2025, Ultragenyx announced that its Phase III Orbit and Cosmic studies failed to achieve statistical significance in reducing annualized fracture rates, causing its stock price to plummet by approximately 42.32% in a single day, from $34.19 to $19.72, reflecting market disappointment in the study outcomes.
- Mereo BioPharma's Reaction: Similarly, Mereo BioPharma announced on December 29, 2025, that its ORBIT and COSMIC studies did not meet the primary endpoint of reducing annualized clinical fracture rates, despite improved bone mineral density, leading to a dramatic decline in its ADS price from $2.31 to $0.29, a drop of over 87.7%, highlighting severe investor confidence erosion.
- Disclosure Issues: The lawsuits allege that both companies provided overly optimistic projections to investors while concealing significant adverse facts related to the study protocols, resulting in shareholders purchasing stocks at artificially inflated prices, raising concerns about corporate governance and transparency.
See More
Class Action Notice for Mereo BioPharma Investors
- Class Action Deadline: Investors in Mereo BioPharma Group plc must apply to be lead plaintiffs by April 6, 2026, to potentially receive compensation without any out-of-pocket costs, indicating a significant impact on investor confidence regarding the company's future.
- False Statements Allegations: The lawsuit alleges that the company misrepresented the expected outcomes of the Phase 3 Orbit and COSMIC studies for setrusumab, leading investors to purchase ADS at inflated prices, highlighting serious deficiencies in the company's transparency and information disclosure practices.
- Law Firm Credentials: The Rosen Law Firm specializes in securities class actions and has recovered over $438 million for investors in 2019 alone, showcasing its proven track record and expertise in handling similar cases, which enhances investor trust in their representation.
- Investor Guidance: The law firm advises investors to select qualified counsel with a successful track record to avoid partnering with inexperienced intermediaries, ensuring they receive the best legal support and potential compensation in the class action.
See More
Class Action Filed Against Mereo BioPharma Group for Securities Violations
- Class Action Initiated: Bronstein, Gewirtz & Grossman LLC has filed a class action lawsuit against Mereo BioPharma Group, seeking damages for investors who purchased securities between June 5, 2023, and December 26, 2025, reflecting strong investor response to potential fraud allegations.
- Allegations of False Statements: The complaint alleges that Mereo provided overly positive statements to investors while concealing significant adverse facts regarding the Phase 3 ORBIT and COSMIC programs, which failed to meet their primary endpoints, potentially undermining investor confidence.
- Call to Action for Investors: Affected investors are encouraged to apply to be lead plaintiffs by April 6, 2026, to share in any potential recovery from the lawsuit, indicating the legal team's commitment to protecting investor rights.
- No-Cost Legal Services: The law firm offers legal representation on a contingency fee basis, meaning they will only charge fees if they successfully recover funds, thereby reducing the legal risk for investors and enhancing the appeal of participating in the lawsuit.
See More
