Mereo Biopharma Group PLC 8-K Filing

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• mreo-20251229.htm (8-K) — 65KB
• mreo-ex99_1.htm (EX-99.1) — 33KB
• 0001193125-25-332520.txt ( ) — 262KB
• mreo-20251229.xsd (EX-101.SCH) — 57KB
• mreo-20251229_htm.xml (XML) — 6KB

01 Other Events

Item 8.01 Other Events. On December 29, 2025, the Company announced the results from the Phase 3 Orbit and Cosmic studies evaluating setrusumab (UX143) in pediatric and young adult patients with osteogenesis imperfecta (OI). Neither study achieved statistical significance against the primary endpoints of reduction in annualized clinical fracture rate compared to placebo or bisphosphonates, respectively. Both studies achieved their secondary endpoints of improvements in bone mineral density (BMD) against comparators (placebo and bisphosphonates) with strong statistical significance. There was no change in the safety profile observed. ORBIT and COSMIC bone mineral density (BMD) improvements In the Orbit study, participants experienced statistically significant and substantial improvements in BMD compared to placebo, at levels consistent with the treatment effect observed in Phase 2 studies. These BMD changes were not accompanied by a corresponding reduction in annualized fracture rates and there was a low fracture rate in the placebo group. In the pediatric Cosmic study, patients had a substantially higher baseline fracture rate compared to the patients enrolled in Orbit. In this younger patient population, meaningful improvements in BMD were associated with a reduction in annualized fracture rate for setrusumab treated patients over bisphosphonate treated patients, though the reduction did not meet statistical significance. Additional analyses on the data across both studies are being conducted, including in other bone health and clinical endpoints beyond fractures.

Forward Looking Statements

Forward Looking Statements This Current Report on Form 8-K contains "forward-looking statements." All statements other than statements of historical fact contained herein are forward-looking statements within the meaning of Section 27A of the Securities Act, and Section 21E of the Exchange Act. Forward-looking statements usually relate to future events and anticipated revenues, earnings, cash flows or other aspects of the Company's operations or operating results. Forward-looking statements are often identified by the words "believe," "expect," "anticipate," "plan," "intend," "foresee," "should," "would," "could," "may," "estimate," "outlook" and similar expressions, including the negative thereof. The absence of these words, however, does not mean that the statements are not forward-looking. These forward-looking statements are based on Mereo's current expectations, beliefs and assumptions concerning future developments and business conditions and their potential effect on Mereo. While management believes that these forward-looking statements are reasonable as and when made, there can be no assurance that future developments affecting Mereo will be those that it anticipates. All of Mereo's forward-looking statements involve known and unknown risks and uncertainties some of which are significant or beyond its control and assumptions that could cause actual results to differ materially from Mereo's historical experience and its present expectations or projections. Such risks and uncertainties include, among others, the uncertainties inherent in the clinical development process; Mereo's reliance on third parties to conduct and provide funding for its clinical trials; Mereo's dependence on enrollment of patients in its clinical trials; and Mereo's dependence on its key executives. You should carefully consider the foregoing factors and the other risks and uncertainties that affect Mereo's business, including those described in the "Risk Factors" section of its latest

01 Financial Statements and Exhibits

Item 9.01 Financial Statements and Exhibits. The following exhibit relating to Item 7.01 shall be deemed to be furnished, and not filed: (d) Exhibits Exhibit No. Description of Exhibit 99.1 Press Release, dated December 29, 2025 . 104 Cover Page Interactive Data File (embedded within the Inline XBRL document).

SIGNATURES

SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the registrant has duly caused this report to be signed on its behalf by the undersigned, hereunto duly authorized. MEREO BIOPHARMA GROUP PLC Date: December 29, 2025 By: /s/ Christine Fox Name: Christine Fox Title: Chief Financial Officer

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