OS Therapies Announces Positive Biomarker Data from Phase 2b Clinical Trial of OST-HER2 in the Prevention or Delay of Recurrent, Fully Resected, Pulmonary Metastatic Osteosarcoma

OS Therapies (NYSE American: OSTX) reported positive biomarker results from its Phase 2b OST-HER2 trial in fully resected, pulmonary metastatic osteosarcoma.

Rhea-AI Summary

OS Therapies (NYSE American: OSTX) reported positive biomarker results from its Phase 2b OST-HER2 trial in fully resected, pulmonary metastatic osteosarcoma. Activation of interferon gamma pathway blood biomarkers correlated with overall survival, distinguishing patients with >=2-year survival from those 1 year. The biomarker strategy was pre-specified based on a 118-patient canine study published February 2025, supporting translational Comparative Oncology. The company is drafting a BLA and targets UK approval by end-Q2 2026, US by end-Q3 2026, and Europe by end-2026. OST-HER2 holds FDA ODD, FDA/EMA Fast Track, and FDA RPDD; PRV eligibility exists if Accelerated Approval occurs before Sept 30, 2026.

Positive

• Interferon gamma biomarkers predicted survival (>=2 years vs <1 year)
• Pre-specified biomarker strategy derived from 118-patient canine study
• Targeted regulatory timelines: UK end-Q2 2026; US end-Q3 2026
• OST-HER2 holds FDA ODD, FDA/EMA Fast Track, and FDA RPDD

Negative

• Regulatory approval dates are company targets, not guarantees
• PRV eligibility conditional on Accelerated Approval before Sept 30, 2026
• BLA and marketing authorizations remain pending and incomplete

Argus Jan 15 session

-5.81% close to close Open Argus

Details

News Market Reaction – OSTX

In the Jan 15 session, OSTX declined 5.81%, reflecting a notable negative market reaction.

Data tracked by StockTitan Argus on the day of publication.

Market Context

The stock moved -5.8% in the session following this news. A negative reaction despite positive bioma...

Analysis

The stock moved -5.8% in the session following this news. A negative reaction despite positive biomarker data would fit prior instances where favorable regulatory updates did not translate into sustained gains. Investors may focus on financing overhang from the shelf and past warrant activity, or on execution and timing risks around multiple planned BLA and MAA submissions. The pattern of divergence on good news could make the timeline to regulatory decisions and any additional capital raises key factors in how sentiment evolved.

Key Figures

Canine trial size: 118 patients Long-term survival cutoff: >=2 years Short-term survival cutoff: <1 year +5 more

Canine trial size

118 patients

Canine metastatic osteosarcoma study published February 2025

Long-term survival cutoff

>=2 years

Definition of long-term survivors in Phase 2b biomarker analysis

Short-term survival cutoff

<1 year

Definition of short-term survivors in Phase 2b biomarker analysis

Target UK approval

End of Q2 2026

Planned OST-HER2 regulatory timeline in the United Kingdom

Target US approval

End of Q3 2026

Planned OST-HER2 regulatory timeline in the United States

Target EU approval

Year-end 2026

Planned OST-HER2 regulatory timeline in Europe

PRV deadline

September 30, 2026

Accelerated Approval by this date could qualify for PRV

Recent PRV sale

$200 million

Most recent Priority Review Voucher sale, January 2026

Historical Context

5 past events · Latest: Jan 14

5 events

1. Jan 14

   Subsidiary S-1 filing

   24h Move

   +0.7%

   Planned OS Animal Health IPO and share distribution to OSTX holders.

2. Jan 12

   Warrant financing

   24h Move

   -7.1%

   Warrant inducement raising $7.53M for runway and filings.

3. Jan 05

   Corporate outlook

   24h Move

   +7.5%

   Outlined 1H 2026 BLA/MAA timelines and key data readouts.

4. Dec 15

   FDA Type C meeting

   24h Move

   -7.7%

   FDA confirmed single-arm data could support Accelerated Approval.

5. Dec 09

   UK MHRA pre-MAA

   24h Move

   +0.0%

   MHRA alignment on CMC and biomarker surrogate endpoint strategy.

24h Move is the share-price change in the day after each event; other market factors may also have contributed.

Key Terms

interferon gamma, biomarkers, comparative oncology, biologics license application (bla), +4 more

8 terms

interferon gamma medical

"Activation of immune blood biomarkers from interferon gamma pathway distinguished long term"

Interferon gamma is a signaling protein made by certain white blood cells that helps coordinate the body's defense against infections and abnormal cells by 'turning on' other immune cells. Investors care because it is used as a target and ingredient in medicines, diagnostics, and clinical trials; results involving it can change a drug’s commercial prospects much like a smoke alarm changing the value of a fire-prevention product.

biomarkers medical

"Activation of immune blood biomarkers in the interferon gamma pathway was predictive"

Biomarkers are measurable indicators found in the body, such as substances in blood or tissues, that reveal information about health or disease. For investors, they can signal how well a medical treatment is working or whether a disease is developing, helping to assess the potential success or risks of healthcare companies or innovations. Think of biomarkers as biological signals that provide clues about a person’s health status.

comparative oncology medical

"demonstrates the translational power of Comparative Oncology in identifying surrogate markers"

Comparative oncology studies cancer across different species—most often using naturally occurring tumors in pets like dogs—to learn how cancers behave and respond to treatments in ways that mirror human disease. For investors, it matters because this cross-species testing can speed up drug development, reveal which therapies are likely to work, and lower the risk and cost of bringing new cancer treatments to market, much like using a rehearsal to improve a final performance.

biologics license application (bla) regulatory

"This biomarker data strengthens our pending Biologics License Application (BLA) submission."

A biologics license application (BLA) is a formal request to a government agency seeking approval to sell a biological medicine, such as vaccines or gene therapies, in the market. It is similar to a detailed report that proves the product is safe, effective, and manufactured properly. For investors, a BLA signifies a critical step toward commercial availability, often impacting a company's valuation and market prospects.

marketing authorisation application regulatory

"planned BLA submission along with its pending Marketing Authorisation Application submissions"

A marketing authorisation application is the formal package a drug or medical-device maker submits to a health regulator to get permission to sell a product. Think of it as an application for a sales license: regulators review safety, effectiveness and manufacturing quality before granting permission. Investors watch these submissions because approval unlocks revenue and reduces development risk, while rejection or delays can materially affect a company’s value and timeline.

orphan disease designation regulatory

"OST-HER2 has received FDA Orphan Disease Designation (ODD) and Fast Track Designation"

A regulatory label granted to a drug or treatment aimed at a rare medical condition, recognizing that few patients need it. It brings incentives such as reduced development costs, regulatory help and a period of protection from direct competition — like a government badge and temporary shield for a small-market product. For investors, the designation can lower risk, speed approval and raise the potential commercial value of a therapy.

fast track designation regulatory

"Orphan Disease Designation (ODD) and Fast Track Designation from FDA & EMA"

Fast track designation is a status the U.S. Food and Drug Administration grants to drugs intended to treat serious conditions and address an unmet medical need. It gives the developer more frequent communication with the FDA and can allow parts of the application to be reviewed on a rolling basis, and it may pave the way to priority review or accelerated approval. It can shorten development timelines, though it does not guarantee approval.

priority review voucher regulatory

"it will become eligible to receive a Priority Review Voucher (PRV) that it intends to sell."

A priority review voucher is a transferable regulatory incentive that lets a company move a future drug or device application to the front of the review line, shortening the review period by several months. For investors it matters because the voucher can speed up market access for a high-value product or be sold to other companies for significant cash, acting like a tradable fast-pass that can accelerate revenue or create immediate financial upside.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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• Activation of immune blood biomarkers from interferon gamma pathway distinguished long term survivors (>=2 years) from short-term survivors (<1year)
• Pre-specified pathway analysis strategy developed as a result of immune biomarker pathway data generated from 118-patient canine metastatic osteosarcoma study published in February 2025 demonstrates translational power of Comparative Oncology to identify surrogate markers of clinical efficacy

New York, New York--(Newsfile Corp. - January 15, 2026) - OS Therapies Inc. (NYSE American: OSTX) ("OS Therapies" or "the Company"), the world leader in listeria-based cancer immunotherapies, today announced positive biomarker data from its Phase 2b clinical trial of OST-HER2 in the prevention or delay of recurrent, fully resected, pulmonary metastatic osteosarcoma (the "Human Metastatic Osteosarcoma Trial"). Activation of immune blood biomarkers in the interferon gamma pathway was predictive of overall survival, distinguishing long term survivors (>=2 years) from short-term survivors (<1year). The Company's pre-specified pathway analysis strategy that was developed as a result of immune biomarker pathway data generated from 118-patient canine metastatic osteosarcoma study published in February 2025 (the "Canine Metastatic Osteosarcoma Trial") demonstrates the translational power of Comparative Oncology in identifying surrogate markers of clinical efficacy for human osteosarcoma clinical development programs.

"Leveraging the power of Comparative Oncology, we were able to train and test potentially predictive biomarkers from the Canine Metastatic Osteosarcoma Trial in order to form a hypothesis to test in a pre-specified way in the Human Metastatic Osteosarcoma Trial," said Paul Romness, MHP, Chairman & CEO of OS Therapies. "We believe the confirmation of this pre-specified pathway analysis in humans adds significant resolution to our clinical data, increasing the clinical interpretability of the 2-year overall survival data for regulatory agencies. The confirmation of a pre-specified canine biomarker pathway being upregulated in a comparable human clinical study population leveraged canine biomarker data to a generate hypothesis that was tested in a pre-specified way and confirmed as a surrogate marker of clinical efficacy. This biomarker data strengthens our pending Biologics License Application (BLA) submission."

The Company is focused on completing the drafting of its planned BLA submission along with its pending Marketing Authorisation Application submissions in the U.K. and Europe. The Company is targeting gaining regulatory approval for OST-HER2 in the United Kingdom by the end of the second quarter of 2026, the United States by the end of the third quarter of 2026 and Europe by year end 2026."

OST-HER2 has received FDA Orphan Disease Designation (ODD) and Fast Track Designation from FDA & EMA and has received Rare Pediatric Disease Designation (RPDD) from FDA. Under the RPDD program, if the Company receives Accelerated Approval prior to September 30, 2026, it will become eligible to receive a Priority Review Voucher (PRV) that it intends to sell. The most recent PRV sale, valued at $200 million, occurred in 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 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
Stephanie Chen
Elev8 New Media
media@ostherapies.com

https://x.com/OSTherapies
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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/280482

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What did OS Therapies announce about OST-HER2 biomarker data on January 15, 2026?

OS Therapies reported interferon gamma blood biomarkers correlated with overall survival in its Phase 2b OST-HER2 trial, distinguishing >=2-year from <1-year survivors.

How does the February 2025 118-patient canine study relate to OSTX human data?

The company pre-specified a pathway analysis based on the canine study and confirmed the same biomarker pathway in the human Phase 2b trial.

What regulatory timelines did OS Therapies (OSTX) provide for OST-HER2 approvals?

The company targets UK approval by end-Q2 2026, US approval by end-Q3 2026, and Europe approval by end-2026.

Is OST-HER2 eligible for a Priority Review Voucher (PRV) and what is its condition?

OST-HER2 is eligible for a PRV only if the company receives Accelerated Approval before Sept 30, 2026; a recent PRV sale was valued at $200 million.

What regulatory designations does OST-HER2 hold as of January 15, 2026?

OST-HER2 has FDA Orphan Disease Designation, FDA and EMA Fast Track Designation, and FDA Rare Pediatric Disease Designation.