OS Therapies Files New Patent Application Covering Biomarkers of the Immune Response to Listeria Monocytogenes

OS Therapies (NYSE American: OSTX) filed a patent application covering a treatment-emergent immune signature tied to Listeria-based OST-HER2 therapy in its Phase 2b trial for preventing or delaying recurrent, fully‑resected pulmonary metastatic osteosarcoma.

Rhea-AI Summary

OS Therapies (NYSE American: OSTX) filed a patent application covering a treatment-emergent immune signature tied to Listeria-based OST-HER2 therapy in its Phase 2b trial for preventing or delaying recurrent, fully‑resected pulmonary metastatic osteosarcoma.

The company says the biomarker met FDA BEST pharmacodynamic/response criteria as a surrogate for 1‑year event‑free survival and 2‑year overall survival, will host an April 2026 call, will file to EMA on April 30, 2026, and aims for a BLA under Accelerated Approval in H2‑2026.

Positive

• Patent application filed covering OST-HER2 immune biomarker signature
• Biomarker correlates with 1‑year EFS and 2‑year overall survival
• EMA market‑access filing scheduled for April 30, 2026
• Company pursuing BLA under FDA Accelerated Approval in H2‑2026
• OST-HER2 holds FDA ODD, FTD and RPDD designations

Negative

• Biomarker correlation reported from Phase 2b; broader validation not disclosed
• Regulatory approvals still pending across FDA, EMA, MHRA and TGA
• Reliance on Accelerated Approval may require confirmatory trials post‑approval

Argus Apr 16 session

+1.45% close to close Open Argus

Details

News Market Reaction – OSTX

On Apr 16, the day this news came out, OSTX closed 1.45% above the previous close.

Data tracked by StockTitan Argus for the Apr 16 session.

Key Figures

1-year EFS endpoint: 1-year event free survival 2-year OS endpoint: 2-year overall survival HER2 positivity rate: over 80% +5 more

1-year EFS endpoint

1-year event free survival

Surrogate clinical endpoint per FDA BEST criteria in Phase 2b

2-year OS endpoint

2-year overall survival

Surrogate clinical endpoint linked to biomarker signature

HER2 positivity rate

over 80%

Metastatic osteosarcoma lesions HER2 positive in cited study

Biomarker responders

100%

Patients with 1-year EFS showing distinct immune signature and 2-year OS

Priority Review Voucher value

$205 million

Most recent publicly disclosed PRV transaction in Feb 2026

EMA filing date

April 30, 2026

First complete OST-HER2 regulatory market access filing

BLA timing

second half of 2026

Target for BLA under Accelerated Approval Program in osteosarcoma

Potential expansion year

2027

Company cites potential jurisdictional expansion beyond U.S. and Europe

Historical Context

5 past events · Latest: Apr 13

5 events

1. Apr 13

   Strategic advisor hire

   24h Move

   +1.5%

   Biotech luminary Robert Langer joins as strategic advisor for listeria pipeline.

2. Apr 08

   Strategic advisor hire

   24h Move

   +1.6%

   Craig Eagle appointed to advise on osteosarcoma regulatory execution and pipeline.

3. Apr 02

   Registered direct offering

   24h Move

   -6.6%

   Completed $5.25M registered direct equity offering with warrants.

4. Mar 31

   Earnings & clinical update

   24h Move

   +6.0%

   Filed Phase 2b data for FDA Pre-BLA and reported 2025 financial results.

5. Mar 27

   Regulatory meetings

   24h Move

   +2.9%

   Secured multi-agency meetings for global confirmatory Phase 3 trial design.

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

Key Terms

biomarker, pharmacodynamic, surrogate clinical endpoint, event free survival, +4 more

8 terms

biomarker medical

"new biomarker signatureBiomarker signature meets pharmacodynamic/response criteria"

A biomarker is a measurable indicator found in the body, such as in blood or tissues, that provides information about health, disease, or how the body responds to treatment. For investors, biomarkers can signal the potential success or risk of medical products or therapies, influencing the value of related companies and industry trends. They act like signals or clues that help assess the progress of medical advancements and their market impact.

pharmacodynamic medical

"Biomarker signature meets pharmacodynamic/response criteria established by FDA's Biomarkers"

Pharmacodynamic describes how a drug acts on the body — the biological effects it produces, how strong those effects are, and how long they last. For investors, pharmacodynamic data show whether a treatment actually works and at what dose, shaping expectations about a drug’s safety, effectiveness, regulatory success and market potential; think of it like testing how well a key turns a lock and whether it reliably opens the door.

surrogate clinical endpoint medical

"for use as a surrogate clinical endpoint of 1-year event free survival"

A surrogate clinical endpoint is a measurable sign or test result—such as a lab value, blood pressure change, or imaging result—used in a clinical trial as a stand-in for a direct patient outcome like survival or symptom relief. Because it can be observed sooner or with fewer patients than the real clinical outcome, regulators may accept it to speed drug or device approval; for investors, reliance on these endpoints can shorten development time and reduce cost but also increases regulatory and commercial risk if the surrogate later fails to predict real patient benefit.

event free survival medical

"surrogate clinical endpoint of 1-year event free survival and 2-year overall survival"

A clinical trial measure that tracks how long patients live without a predefined bad outcome—such as the disease getting worse, a return of the disease, or death—after starting a treatment. Investors watch it because longer event‑free survival suggests the treatment is providing meaningful benefit, which can boost likelihood of regulatory approval, payer coverage, and commercial success; think of it like how long a repaired car runs without needing another fix, signaling reliability and value.

overall survival medical

"surrogate clinical endpoint of 1-year event free survival and 2-year overall survival"

Overall survival is the average or median length of time patients remain alive after starting a treatment or entering a clinical study, measured regardless of cause of death. Investors care because it is a clear, hard measure of a therapy’s real-world benefit — like timing how long a new battery actually runs — and strong improvements in overall survival can drive regulatory approval, market adoption and revenue potential.

biologics license application regulatory

"support a BLA submission under FDA's Accelerated Approval Program"

A biologics license application is a formal request submitted to regulatory authorities seeking approval to market a new biological medicine, such as vaccines or treatments made from living organisms. It is a comprehensive review process that evaluates the safety, effectiveness, and manufacturing quality of the product. For investors, receiving approval signals that a biological therapy can be sold to the public, potentially leading to revenue growth and market success.

accelerated approval program regulatory

"to support a BLA submission under FDA's Accelerated Approval Program"

A regulatory pathway that lets a drug or treatment reach the market sooner for serious or life‑threatening conditions based on early signs of benefit (such as lab tests or short‑term results) rather than long‑term proof. It matters to investors because it can accelerate revenue and competitive advantage but carries higher risk: the approval depends on follow‑up studies, and if those fail regulators can withdraw the approval, which can sharply affect a company’s value.

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.

See more from StockTitan in Google Search and AI answers. Adds StockTitan as a preferred source · opens Google

Add on Google Not now

• New patent application covers treatment-emergent immune signature related to 'turning cold tumors hot' and the activation of targeted cytotoxic cellular immune responses
• Company to host conference call later in April 2026 to review new biomarker signature
• Biomarker signature meets pharmacodynamic/response criteria established by FDA's Biomarkers, EndpointS and other Tools (BEST) program for use as a surrogate clinical endpoint of 1-year event free survival and 2-year overall survival in OST-HER2's Phase 2b trial in the prevention of delay of recurrent, fully-resected, pulmonary metastatic osteosarcoma to support a BLA submission under FDA's Accelerated Approval Program

New York, New York--(Newsfile Corp. - April 16, 2026) - OS Therapies, Inc. (NYSE American: OSTX) ("OS Therapies" or "the Company"), the world leader in gene-edited, listeria-based cancer immunotherapies, today announced that it has filed a new patent application covering a unique immune signature in response to treatment with therapeutic candidates developed from the Company's proprietary Listeria monocytogenes platform ('Listeria') based on new biomarker data from the Company's Phase 2b trial of OST-HER2 in the prevention or delay of recurrent, fully-resected, pulmonary metastatic osteosarcoma. Filed claims include treatment with Listeria leading to the downregulation of genes associated with tumor and circulating tumor cell immune evasion in combination with the upregulation of genes associated with cytotoxic cellular immune activation leads to improved anti-tumor cellular immunity activation. The Company will host a conference call later in April 2026 to review OST-HER2 Phase 2b's new treatment response biomarker signature data showing correlation with clinical outcomes, and its regulatory implications in upcoming Q2-2026 meetings and regulatory submissions with the U.S. Food & Drug Administration (FDA), the European Medicines Agency (EMA), the U.K. Medicines and Healthcare products Regulatory Agency (MHRA) and the Australian Therapeutic Goods Administration (TGA). The Company will complete the first complete OST-HER2 regulatory market access filing in the world to the EMA, at its request, on April 30, 2026.

"The biomarker data from patients who responded to OST-HER2 treatment shows tremendous innate and adaptive immune responses that result in a significantly improved ability to fight cancer," said Paul Romness, MPH, Chair & CEO of OS Therapies. "While not all metastatic osteosarcoma is HER2 positive, a recently published study reported that over 80% of the patients were found to have HER2 positive metastatic lesions^[1]. In our Phase 2b trial, 100% of the patients that did achieve 1-year event free survival (EFS) exhibited the distinct immune signature covered in our patent application and went of to achieve 2-year overall survival. We believe this meets the pharmacodynamic/response biomarker criteria outlined in the U.S. Food & Drug Administration's (FDA)'s Biomarkers, EndpointS, and other Tools (BEST)^[2] glossary as a surrogate clinical endpoint to support a Biologics License Application under the Accelerated Approval Program^[3]. This pharmacodynamic/response biomarker also provides us with a strong basis to think about additional clinical applications of OST-HER2 beyond osteosarcoma, such as in HER2 positive breast cancer and bladder cancer.

Mr. Romness continued, "Notwithstanding the potential for future indication expansion, we are now laser focused on our packed Q2-2026 regulatory meeting schedule with FDA, EMA, MHRA and TGA in preparation for gaining accelerated market access for OST-HER2 in the fully-resected pulmonary metastatic setting later this year in the U.S., Europe and the U.K. with the potential to expand beyond these jurisdictions in 2027."

OST-HER2 has received Orphan Drug Designation (ODD), Fast Track Designation (FTD) and Rare Pediatric Disease Designation (RPDD) from the FDA, and ODD, FTD and ATMP from the EMA. Under the RPDD program, if the Company receives a Biologics License Application (BLA) in the United States, it will become eligible to receive a Priority Review Voucher (PRV) that it intends to sell. The most recent publicly disclosed PRV transaction occurred in February 2026 at a reported value of $205 million. The Company is seeking to obtain a BLA under the Accelerated Approval Program for OST-HER2 in osteosarcoma in the second half of 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 Orphan Drug Designation (ODD), Fast Track Designation (FTD) and Rare Pediatric Disease Designation (RPDD) from the U.S. Food & Drug Administration and has received ODD, FTD and ATMP from the 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 and the overall survival (OS) secondary endpoint. The Company anticipates receiving a Biologics License Application (BLA) from 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. The Company also anticipates receiving Conditional Marketing Authorisations from the U.K.'s Medicines and Healthcare products Regulatory Agency and the EMA for OST-HER2 in 2026. 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. The Company also anticipates reading out data from a Phase 1b study of OST-504 in castration resistant prostate cancer in the first half of 2026.

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 our expected to provide cash runway into 2027, the intended use of net proceeds from the offering, the potential 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 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
https://www.instagram.com/ostherapies/
https://www.facebook.com/OSTherapies/
https://www.linkedin.com/company/os-therapies/

---

^[1] https://ascopubs.org/doi/10.1200/OA-25-00094

^[2] https://www.fda.gov/drugs/biomarker-qualification-program/about-biomarkers-and-qualification

^[3] https://www.fda.gov/drugs/nda-and-bla-approvals/accelerated-approval-program

To view the source version of this press release, please visit https://www.newsfilecorp.com/release/292852

FAQ

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

What patent did OS Therapies (OSTX) file on April 16, 2026?

They filed a patent application covering a treatment‑emergent immune signature linked to Listeria‑based OST‑HER2 therapy. According to the company this signature reflects gene downregulation tied to immune evasion and upregulation tied to cytotoxic immune activation in Phase 2b responders.

How does the OST-HER2 biomarker relate to survival outcomes in OSTX's Phase 2b trial?

The biomarker reportedly correlated with clinical outcomes: 100% of patients with 1‑year EFS showed the signature and achieved 2‑year overall survival. According to the company, this meets FDA BEST pharmacodynamic/response criteria as a surrogate endpoint.

When will OS Therapies (OSTX) file regulatory paperwork with the EMA and FDA?

The company will complete its first EMA market‑access filing on April 30, 2026 and is planning Q2‑2026 regulatory meetings. According to the company, it targets a BLA submission under Accelerated Approval in H2‑2026.

What regulatory designations does OST-HER2 have that affect OSTX's pathway?

OST-HER2 holds FDA Orphan Drug, Fast Track and Rare Pediatric Disease designations and EMA ODD, FTD and ATMP designations. According to the company, RPDD eligibility could allow a Priority Review Voucher if a U.S. BLA is accepted.

What is the commercial implication of a Priority Review Voucher for OSTX?

A PRV could have material value if obtained and sold; a recent PRV transaction was reported at $205 million in February 2026. According to the company, it intends to sell any PRV earned under RPDD rules.