OS Therapies Achieves Statistically Significant Benefit for OST-HER2-Treated Patients in Interim 3-Year Overall Survival Analysis of Phase 2b Pulmonary Metastatic Osteosarcoma Trial
Interim Phase 2b data show improved 3-year survival for OST-HER2 and new VAT refunds help fund a U.K.-based confirmatory Phase 3 trial.
Rhea-AI Summary
OS Therapies (OSTX) reported an interim 3-year overall survival rate of 71.2% for OST-HER2-treated patients in its Phase 2b pulmonary metastatic osteosarcoma trial, versus 45.8% in a comparable combined historical control group (p = 0.002).
The analysis covers 41 enrolled patients, with two not yet at the 3-year timepoint and six lost to follow-up. The company said these data support ongoing regulatory interactions aimed at early market access, including a planned Biologics License Application (BLA) under the FDA’s Accelerated Approval Program and Conditional Marketing Authorization Applications (CMAAs) in the U.K., Europe and Australia in the fourth quarter of 2026, targeting commercial availability in 2027.
OS Therapies also received $3.15 million in VAT refunds into its U.K. subsidiary and expects at least an additional $7.2 million in refundable VAT and R&D tax credits, which are earmarked to fund initiation of a confirmatory Phase 3 trial in the U.K. OST-HER2 has ODD, FTD and RPDD in the U.S. and ODD, FTD and ATMP in Europe, and a rolling BLA submission that began in January 2026.
Positive
- 3-year overall survival 71.2% vs. 45.8% for OST-HER2-treated patients compared with a combined historical control (p = 0.002)
- 41 patients enrolled in the Phase 2b metastatic osteosarcoma trial providing the interim 3-year overall survival analysis
- $3.15 million in VAT refunds received into OS Therapies UK, Ltd. to support operations
- At least $7.2 million in additional refundable VAT and R&D tax credits eligibility confirmed, earmarked for the U.K. Phase 3 trial
- Multiple regulatory designations for OST-HER2, including ODD, FTD and RPDD from FDA and ODD, FTD and ATMP from EMA
- Rolling BLA submission for OST-HER2 underway since January 2026 with a goal of Accelerated Approval and CMAAs in Q4 2026
Negative
- Six patients in the Phase 2b dataset are reported as lost to follow-up
- Two enrolled patients have not yet reached the 3-year timepoint, so the survival analysis is interim
- $7.2 million in additional VAT and R&D tax credits remain pending, not yet received
- The company notes there can be no assurance of realizing comparable value, if any, from any future Priority Review Voucher sale
News Explained
The received
Sources and calculations
- OS Therapies press release (2026-09-08)
- Second-quarter 2026 fundamentals (2026-06-30)
- Available liquidity against the last reported quarterly operating outflow, in days at that rate $205,035 / ($5,532,872 / 91) = 3.4 days
Details
Market Reaction – OSTX
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Key Figures
- 3-year overall survival
- 71.2%
- OST-HER2-treated patients
- Historical control survival
- 45.8%
- Comparable combined historical control group
- P-value
- p = 0.002
- Interim 3-year overall survival analysis
- Trial enrollment
- 41 patients
- Phase 2b metastatic osteosarcoma trial
- Lost to follow-up
- 6 patients
- Phase 2b interim analysis
- VAT refund received
- $3.15 million
- Received by OS Therapies UK, Ltd.
- Refundable VAT and R&D tax credits pending
- $7.2 million
- Additional refund requests
- Target submission period
- Fourth quarter of 2026
- BLA and CMAA submissions
Historical Context
-
Reported 2.5-year overall survival benefit and regulatory progress for OST-HER2
-
Received FDA meeting to review 2.5-year survival data and regulatory pathway
24h Move is the share-price change in the day after each event; other market factors may also have contributed.
Key Terms
overall survival medical
biologics license application regulatory
accelerated approval program regulatory
orphan drug designation regulatory
priority review voucher regulatory
AI-generated analysis. How Rhea-AI works. Not financial advice.
71.2% 3-year overall survival for OST-HER2-treated patients vs.45.8% comparable combined historical control (p = 0.002)- The two remaining patients who have not yet reached the 3-year timepoint from enrollment have trial monitoring visits scheduled for September 2026 and early October 2026
- Company receives
$3.15 million in VAT refunds into OS Therapies UK, Ltd. subsidiary, with an additional$7.2 million in refundable VAT and R&D Tax Credits pending
New York, New York and Rockville, Maryland--(Newsfile Corp. - September 8, 2026) - OS Therapies, Inc. (NYSE American: OSTX) ("OS Therapies" or the "Company"), the world leader in gene-edited, Listeria-based cancer immunotherapies, today announced a statistically significant benefit for OST-HER2-treated patients in an interim 3-year overall survival data analysis when compared with a combined published historical control arm being used for regulatory interactions. The analysis is from the Company's Phase 2b trial for the prevention or delay of recurrence in patients with fully resected, pulmonary metastatic osteosarcoma (the "Metastatic Osteosarcoma Program").
The interim 3-year overall survival rate among OST-HER2 treated patients was
Data Table and Kaplan-Meier Curve
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"We believe the increasing survival benefit as time goes on for OST-HER2 treated patients when compared with any and all available published literature in fully resected metastatic osteosarcoma patients, including data published as recently as 2026, presents a compelling case for early market access for osteosarcoma patients who have not seen a new drug approved in the last forty years," said Dr. Craig Eagle, Chief Medical Advisor and Director of OS Therapies.
"Persistence of therapeutic benefit on extended follow-up is typical of the "tail-effect" characteristic of cancer immunotherapies. As we prepare to complete the final data analysis in the next month while we continue our ongoing engagement with regulators worldwide, we believe that the 3-year survival endpoint that the European Medicines Agency (EMA) and the U.K.'s Medicines and Healthcare products Regulatory Agency (MHRA) have accepted as suitable for early market access decisions will also be acceptable to the U.S. Food & Drug Administration (FDA) to support a Biologics License Application (BLA) under the Accelerated Approval Program. We intend to complete regulatory approval submissions to FDA, MHRA, EMA and Australia's Therapeutic Goods Administration (TGA) in months ahead with a view towards making the drug commercially available for patients in 2027," continued Dr. Eagle.
Concurrent with this announcement, the Company announced that it has received
"Following receipt of the first
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 is granted a BLA in the United States, it will become eligible to receive a Priority Review Voucher (PRV) that it intends to sell. The most recent PRV sale occurred in August 2026 for
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 gene-edited, 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 is designed to target two mutated extracellular epitopes and one mutated intracellular epitope of the HER2 oncogene, requiring only one of these three epitopes to be present in a tumor (or micro-metastasis) to trigger the desired immune response. 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 Advanced Therapy Medicinal Products (ATMP) from the European Medicines Agency.
The Company reported positive data in its Phase 2b clinical trial of OST-HER2 in the prevention or delay of recurrence in fully resected, pulmonary metastatic osteosarcoma, demonstrating clinically significant benefit in the 12-month event free survival (EFS) primary endpoint of the study and the overall survival (OS) secondary endpoint. The Company is seeking 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 Authorisation Applications 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 was previously conditionally approved by the U.S. Department of Agriculture for the treatment of canines with osteosarcoma. The Company has also completed dosing in a Phase 1 study of OST-504 for castration-resistant prostate cancer.
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 silicon 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 regarding future expectations, plans, prospects or performance, as well as any other statements that are not historical facts, may constitute forward-looking statements within the meaning of the federal securities laws. Forward-looking statements are generally identified by words such as "anticipate," "believe," "could," "expect," "intend," "may," "plan," "potential," "should," "will" and similar expressions, although not all forward-looking statements contain these words. These statements are based on the current expectations and assumptions of OS Therapies and its management and are subject to risks and uncertainties that could cause actual results to differ materially from those expressed or implied by such forward-looking statements. Such risks and uncertainties include, but are not limited to, the Company's expectations regarding its cash runway; the timing, amount and receipt of VAT refunds and R&D tax credits; the Company's ability to obtain additional financing on acceptable terms or at all; the timing and outcome of regulatory submissions and potential approval of OST-HER2 by the U.S. Food and Drug Administration and applicable foreign regulatory authorities; and other risks and uncertainties described under the heading "Risk Factors" in the Company's most recent Annual Report on Form 10-K and in its other filings with the Securities and Exchange Commission. The forward-looking statements contained in this press release speak only as of the date of this press release, and OS Therapies undertakes no obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by applicable law.
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/
To view the source version of this press release, please visit https://www.newsfilecorp.com/release/313297
FAQ
What is OST-HER2 and how is it designed to treat metastatic osteosarcoma?
OST-HER2 is an immunotherapy that uses gene-edited, Listeria-based technology to stimulate an immune response against the HER2 protein. It is designed to target two mutated extracellular epitopes and one mutated intracellular epitope of the HER2 oncogene, requiring only one of these three epitopes to be present in a tumor or micro-metastasis to trigger the intended immune response. The current Phase 2b program focuses on preventing or delaying recurrence in fully resected, pulmonary metastatic osteosarcoma.
How does OS Therapies plan to use the VAT refunds and tax credits it has secured or expects?
The company has received $3.15 million in VAT refunds into OS Therapies UK, Ltd. and has confirmed eligibility for at least an additional $7.2 million in refundable VAT and R&D tax credits. These funds are earmarked to initiate and support the U.K. portion of the confirmatory Phase 3 Metastatic Osteosarcoma Program trial, which is required to be underway prior to regulatory decisions on a BLA under the Accelerated Approval Program and on CMAAs in the U.K., Europe and Australia.
What is the planned scope and timing of the confirmatory Phase 3 trial for OST-HER2?
The confirmatory Phase 3 trial for the Metastatic Osteosarcoma Program is set to commence in the U.K. following an upcoming meeting with the MHRA. Initial trial opening will be limited to the U.K. because the MHRA is allowing use of existing Phase 2 drug product to start the Phase 3 study. This trial is required to be initiated before an FDA decision on a BLA under the Accelerated Approval Program and before MHRA, EMA and TGA decisions on Conditional Marketing Authorization Applications.
What regulatory milestones and timelines is OS Therapies targeting for OST-HER2?
OS Therapies is seeking to obtain a Biologics License Application (BLA) approval under the FDA Accelerated Approval Program and Conditional Marketing Authorization Applications (CMAAs) in Europe, the U.K. and Australia for OST-HER2 in metastatic osteosarcoma in the fourth quarter of 2026. The company has resubmitted a Regenerative Medicine Advanced Therapy (RMAT) request, had its Commissioner's National Priority Review Voucher letter of intent accepted by FDA, and intends to request rolling review of the ongoing BLA submission after a mid-September 2026 FDA Type C Statistical Methods Meeting. The company aims to make the drug commercially available for patients in 2027 if approvals are obtained.
What potential financial benefit could a Priority Review Voucher provide to OS Therapies?
Under the Rare Pediatric Disease Designation (RPDD) program, if OS Therapies is granted a BLA for OST-HER2 in the United States, it would become eligible to receive a Priority Review Voucher (PRV), which it intends to sell. The announcement notes that the most recent PRV sale in August 2026 was for $220 million, but also states that there can be no assurance the company would realize a comparable value, if any, from any future PRV sale.