OS Therapies Announces Successful pre-Marketing Authorisation Application Meeting with UK MHRA Regarding the Phase 2b Clinical Trial of OST-HER2 in the Prevention or Delay of Recurrent, Fully Resected, Pulmonary Metastatic Osteosarcoma
Rhea-AI Summary
OS Therapies (NYSE: OSTX) reported a successful pre-MAA meeting with the UK MHRA on December 9, 2025, for the Phase 2b OST-HER2 program targeting prevention or delay of recurrent, fully resected, pulmonary metastatic osteosarcoma.
The company said it achieved alignment on non-clinical, CMC and post-market confirmatory study design, advanced a biomarker correlation as a pre-specified surrogate efficacy endpoint tied to 2-year overall survival, and reiterated a target to submit a conditional MAA by end of January 2026. OS Therapies is awaiting input from a December 11, 2025 FDA Type C meeting before initiating the biomarker analysis for potential Accelerated Approval support.
Positive
- Alignment achieved on non-clinical, CMC, and confirmatory design
- Biomarker advanced as pre-specified surrogate tied to 2-year OS
- Company reiterated conditional MAA target by end of January 2026
Negative
- Biomarker analysis pending FDA feedback from December 11, 2025 meeting
- Regulatory path relies on conditional MAA and surrogate endpoint
News Market Reaction
On the day this news was published, OSTX declined NaN%, reflecting a moderate negative market reaction.
Data tracked by StockTitan Argus on the day of publication.
Key Figures
Market Reality Check
Peers on Argus
OSTX gained 2.08% while peers showed mixed moves: BYSI +3.66%, IMMX +4.41%, ANL -14.56%, ACET -2.93%, ATHE -1.5%, pointing to a stock-specific reaction to the regulatory update.
Historical Context
| Date | Event | Sentiment | Move | Catalyst |
|---|---|---|---|---|
| Dec 05 | Regulatory update | Positive | +5.5% | FDA fee waiver and EMA Union Marketing Authorisation eligibility for OST-HER2. |
| Nov 25 | Naming / regulatory prep | Positive | +4.7% | WHO assigns INN name and company reiterates multi-region filing timelines. |
| Nov 21 | Analyst update | Positive | +5.6% | Coverage note highlighting strong Phase 2b survival data and 1H26 spinoff plan. |
| Nov 20 | Spinoff announcement | Positive | -1.8% | Plan to spin off OS Animal Health with direct equity to OSTX holders. |
| Nov 17 | Earnings and update | Neutral | -5.0% | Q3 2025 financials plus clinical and regulatory timeline for OST-HER2. |
OSTX has generally reacted positively to regulatory and program advancement news, with one divergence on the OS Animal Health spinoff announcement.
Over recent months, OS Therapies has steadily advanced OST-HER2 toward approval. On Nov 17, 2025, Q3 results highlighted statistically significant survival data and financing actions. Subsequent updates included the planned OS Animal Health spinoff, progressing regulatory designations and fee waivers, and confirmation of EU and UK pathways with targeted filing dates in January–February 2026. Today’s MHRA pre-MAA alignment fits this sequence of regulatory de-risking for the Metastatic Osteosarcoma Program.
Regulatory & Risk Context
The company has an effective S-3 shelf filed on Aug 8, 2025 allowing issuance of up to $100,000,000 in securities, plus an at-the-market prospectus for up to $18,000,000 of common stock. Two prospectus supplements (424B5, 424B7) have been filed, indicating the shelf is an active capital-raising tool that could be used alongside ongoing clinical and regulatory milestones.
Market Pulse Summary
This announcement strengthens the OST-HER2 regulatory story by confirming MHRA alignment on non-clinical, CMC, biomarker endpoints, and confirmatory study design, while reiterating a conditional MAA target by end of January 2026. It builds on earlier FDA and EMA progress for the Metastatic Osteosarcoma Program. Investors may monitor the upcoming December 11, 2025 FDA Type C meeting, subsequent biomarker analysis, and any capital raises under the existing $100,000,000 shelf as key follow-on developments.
Key Terms
marketing authorisation application regulatory
mhra regulatory
phase 2b medical
biomarker medical
surrogate clinical efficacy endpoint medical
biologics licensing application regulatory
accelerated approval program regulatory
AI-generated analysis. Not financial advice.
- Alignment achieved on all key points surrounding non-clinical, CMC and post-market authorization confirmatory study design
- Biomarker data advanced as key pre-specified surrogate clinical efficacy endpoint, with pending analysis awaiting alignment with US FDA on biomarker statistical analysis plan to be discussed at upcoming December 11, 2025 FDA Type C Meeting
- Company reiterates end of January 2026 timeline for MAA submission
New York, New York--(Newsfile Corp. - December 9, 2025) - OS Therapies Inc. (NYSE American: OSTX) ("OS Therapies" or "the Company"), the world leader in listeria-based cancer immunotherapies, today announced that it held a successful pre-Marketing Authorisation Application (MAA) with the United Kingdom (UK) Medicines and Healthcare Products Regulatory Agency (MHRA) regarding the Phase 2b human clinical trial of OST-HER2 in the prevention or delay of recurrent, fully-resected, pulmonary metastatic osteosarcoma (the 'Metastatic Osteosarcoma Program'). The Company achieved full alignment with its pre-meeting objectives related to non-clinical, CMC (chemistry, manufacturing, and controls) and post-market authorization confirmatory study design.
Additionally, the Company advanced the correlation of upregulated immune response biomarkers shown to be activated in OST-HER2 treated canine patients who achieved long term survival with 2-year overall survival data from the OST-HER2 Phase 2b human clinical trial as a surrogate clinical efficacy endpoint to further support the approval of a conditional MAA in the United Kingdom. The Company is awaiting feedback from its upcoming December 11, 2025 meeting with United States Food & Drug Administration (FDA) before initiating the proposed biomarker data analysis to ensure that the analysis is pre-specified, thereby making the resulting data suitable to support a Biologics Licensing Application (BLA) under the Accelerated Approval Program ('Accelerated Approval') in the United States.
"We were pleased with the insightful feedback from our colleagues at UK MHRA during yesterday's pre-MAA meeting," said Paul Romness, Chairman & CEO of OS Therapies. "Their perspective will be very helpful as we finalize preparations for our upcoming Type C Meeting with US FDA on Thursday."
The Company reiterated that it expects to submit a conditional MAA for the Metastatic Osteosarcoma Program to MHRA by the end of January 2026.
About OS Therapies
OS Therapies is a clinical stage oncology company focused on the identification, development, and commercialization of treatments for Osteosarcoma (OS) and other solid tumors. The Company is the world leader in listeria-based cancer immunotherapies. OST-HER2, the Company's lead asset, is an immunotherapy leveraging the immune-stimulatory effects of Listeria bacteria to initiate a strong immune response targeting the HER2 protein. OST-HER2 has received Rare Pediatric Disease Designation (RPDD) from the U.S. Food & Drug Administration and Fast-Track and Orphan Drug designations from the U.S. FDA and European Medicines Agency. The Company reported positive data in its Phase 2b clinical trial of OST-HER2 in recurrent, fully resected, lung metastatic osteosarcoma, demonstrating statistically significant benefit in the 12-month event free survival (EFS) primary endpoint of the study. The Company anticipates submitting a Biologics Licensing Application (BLA) to the U.S. FDA for OST-HER2 in osteosarcoma in the First Quarter of 2026 and, if approved, would become eligible to receive a Priority Review Voucher that it could then sell. OST-HER2 has completed a Phase 1 clinical study primarily in breast cancer patients, in addition to showing preclinical efficacy data in various models of breast cancer. OST-HER2 has been conditionally approved by the U.S. Department of Agriculture for the treatment of canines with osteosarcoma.
In addition, OS Therapies is advancing its next-generation Antibody Drug Conjugate (ADC) and Drug Conjugates (DC), known as tunable ADC (tADC), which features tunable, tailored antibody-linker-payload candidates. This platform leverages the Company's proprietary silicone Si-Linker and Conditionally Active Payload (CAP) technology, enabling the delivery of multiple payloads per linker. For more information, please visit www.ostherapies.com.
Forward-Looking Statements
Statements in this press release about future expectations, plans and prospects, as well as any other statements regarding matters that are not historical facts, may constitute forward-looking statements within the meaning of the federal securities laws. These forward-looking statements and terms such as "anticipate," "expect," "intend," "may," "will," "should" or other comparable terms involve risks and uncertainties because they relate to events and depend on circumstances that will occur in the future. Those statements include statements regarding the intent, belief or current expectations of OS Therapies and members of its management, as well as the assumptions on which such statements are based. OS Therapies cautions readers that forward-looking statements are based on management's expectations and assumptions as of the date of this press release and are subject to certain risks and uncertainties that could cause actual results to differ materially, including, but not limited to the approval of OST-HER2 by the U.S. FDA and other risks and uncertainties described in "Risk Factors" in the Company's most recent Annual Report on Form 10-K, most recent Quarterly Report on Form 10-Q and other subsequent documents the Company files with the Securities and Exchange Commission. Any forward-looking statements contained in this press release speak only as of the date hereof, and, except as required by the federal securities laws, OS Therapies specifically disclaims any obligation to update any forward-looking statement, whether as a result of new information, future events or otherwise.
OS Therapies Contact Information:
Investor Relations
Harrison Seidner, PhD
WaterSeid Partners
OSTX@waterseid.com
Public Relations
Jessica Reilly
Elev8 New Media
media@ostherapies.com
https://x.com/OSTherapies
https://www.instagram.com/ostherapies/
https://www.facebook.com/OSTherapies/
https://www.linkedin.com/company/os-therapies/
To view the source version of this press release, please visit https://www.newsfilecorp.com/release/277410
FAQ
What did OS Therapies (OSTX) announce about the OST-HER2 Phase 2b trial on December 9, 2025?
When does OS Therapies (OSTX) expect to submit the conditional MAA to MHRA?
How does the December 11, 2025 FDA Type C meeting affect OSTX's biomarker analysis?
What surrogate efficacy endpoint did OS Therapies (OSTX) advance for OST-HER2?
Does the OSTX announcement guarantee regulatory approval for OST-HER2?
