OS Therapies Third Quarter 2026 Corporate Outlook

Upcoming Type B Statistical Methods Meeting expected to set stage for FDA to align with EMA and MHRA on use of Fall 2026 3-year overall survival data combined with biomarkers to support early market access

New York, New York and Rockville, Maryland--(Newsfile Corp. - July 6, 2026) - OS Therapies, Inc. (NYSE American: OSTX) ("OS Therapies" or "the Company"), the world leader in gene-edited, Listeria-based cancer immunotherapies, today provides a third quarter 2026 corporate outlook. The outlook focuses on upcoming clinical and regulatory milestones for the Company's lead program OST-HER2 in the prevention or delay of recurrence in fully resected, pulmonary metastatic osteosarcoma (the "Metastatic Osteosarcoma Program"), advancements with the Company's animal health-focused subsidiary OS Animal Health, Inc. (OSAH) and the Company's financial position as key regulatory and corporate milestones come into focus.

OST-HER2 Metastatic Osteosarcoma Program

OS Therapies recently announced full alignment with the European Medicines Agency (EMA), the U.K.'s Medicines and Healthcare products Regulatory Agency (MHRA) and Australia's Therapeutic Goods Administration (TGA) with respect to the necessary requirements to be granted Conditional Marketing Authorisation Applications (CMAAs). The key outstanding milestones are 3-year overall survival data, which EMA, MHRA and TGA have aligned around to support early market access, and the Pediatric Investigation Plans (PIP) for each jurisdiction. Prior to being granted CMAAs in Europe, the U.K. or Australia, the Company must have commenced a confirmatory Phase 3 clinical study. This Phase 3 study is expected to initiate towards the end of the third quarter of 2026, initially in Australia only and after early market access is decided upon then in the U.K., Europe and the United States. MHRA and TGA have both agreed to allow the Company to initiate the Phase 3 study with the same OST-HER2 drug product batch that was used in the Phase 2b trial and is currently being administered to Expanded Access patients in the United States.

Full alignment has been reached with EMA, MHRA and TGA in the following areas:

• Non-Clinical
• Chemistry, Manufacturing and Controls (CMC)
• Clinical Safety
• Confirmatory Phase 3 protocol design
• Historical Control Comparator
• Initiation of the confirmatory Phase 3 protocol with existing Phase 2 drug product

OS Therapies was granted Advanced Therapy Medicinal Products (ATMP) designation in Europe and the U.K., which permitted access to additional resources from local regulators to support CMAA submissions. The Company is making significant progress towards alignment on the PIP – including a first round of positive feedback from the EMA PDCO - and has received a submission window of September 30, 2026 from EMA for the CMAA. With MHRA and TGA, the Company is in ongoing dialogue to identify the earliest possible date to complete CMAA submissions and is making significant progress towards PIPs.

"Given that 100% of patients who achieved 1-year event free survival (EFS) also achieved overall survival at the 2-year and 2.5-year timepoints, and the knowledge that 100% of patients who did not achieve 1-year EFS while achieving 2-year overall survival also achieved 2.5-year overall survival, we believe the sustained clinical benefit data package emerging for OST-HER2 will be compelling for regulators in comparison with the bleak 3-year overall survival outlook metastatic osteosarcoma patients have," said Dr. Craig Eagle, Chief Medical Advisor and member of the OS Therapies Board of Directors. "While the 1-year EFS data favored OST-HER2-treated patients in a statistically significant manner when compared with historical control data, the biomarker data was highly correlated with 2.5 year overall survival."

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As a result of the initiation of the CMAA process with EMA, coordination has begun between EMA and the U.S. Food & Drug Administration (FDA) with respect to the OST-HER2 regulatory dossier. OS Therapies completed the submission to FDA of the non-clinical and clinical Biologics License Application (BLA) modules in January 2026, and has since completed a Type C Phase 3 protocol design meeting where alignment was achieved on the design of the Phase 3 protocol, as well as alignment on outstanding non-clinical, CMC and clinical safety matters. The Company recently released 2.5-year overall survival clinical efficacy data and is awaiting the date for the requested Type B Statistical Methods meeting being scheduled to align on the methods to evaluate clinical efficacy for the 2.5-year timepoint, the use of historical control and/or OST-400 as appropriate comparator(s) to interpret clinical efficacy, Rolling Review and Regenerative Medicine Advanced Therapy (RMAT) designation. OS Therapies expects this meeting to set the stage for 3-year overall survival data to be used to support the complete BLA submission. Following that Type B Statistical Methods meeting, the Company expects to hold its previously announced invited Type B Pre-BLA meeting in early Fall of 2026, following the completion of the remaining aspects of the BLA submission, to review the entire BLA dossier in an effort to be granted early market access under Accelerated Approval in the U.S.. FDA accepted the Company's letter of intent for the Commissioner's National Priority Review Voucher (CNPV) program in January 2026.

OSAH Clinical, Regulatory and Corporate Progress

The Company recently announced the peer-reviewed publication of new data showing OST-HER2 combined with radiation significantly improved survival in frontline canine osteosarcoma when compared against radiation alone. This adds to previously published data showing that OST-HER2 was effective in treating fully resected metastatic osteosarcoma, as well as unresectable metastatic osteosarcoma when compared with the current standards of care. Canine osteosarcoma data is what originally catalyzed the OST-HER2 human clinical development program.

Following CMC alignment with FDA, EMA, MHRA and TGA, the Company is now in a strong position to review with the U.S. Department of Agriculture (USDA) its regulatory strategy to bring OST-HER2 back into the market to treat canine osteosarcoma. The Company expects to hold a meeting with USDA in the summer of 2026 to review the program and gain alignment on OST-HER2's path to return to the market for canine osteosarcoma. Following that meeting, the Company expects to launch a crowdfunding round in order to expand OSAH's shareholder base prior to completing its previously announced 'go-public' transaction.

OSAH confidentially filed a registration statement on Form S-1 in January 2026 in support of its 'go-public' strategy. The Company reiterates that it intends to grant shares of OSAH to shareholders of OS Therapies.

OS Therapies Financial Position

OS Therapies recently announced that it has entered into a $10 million line of credit (LOC) supported by its OS Therapies U.K., Ltd subsidiary's value added tax (VAT) reimbursements and Research and Development (R&D) Tax Credits. Each draw taken from the LOC is to be repaid within 9 months of issuance, with repayment of the first draw of $1.6 million received by the Company on July 2, 2026 expected no later than April 2, 2027. The Company currently has $5.6 million in outstanding combined VAT and R&D Tax Credits, with an additional $4.6 million expected to be accrued by year-end 2026. The Company did not provide security interest in its intellectual property.

Simultaneously, OS Therapies significantly reduced its expenses in the second quarter of 2026 when compared with the first quarter of 2026 largely driven by completion of biomarker-related expenses that were incurred entirely in the first quarter alongside significant expenses associated with preparing regulatory dossiers to support the submission of the non-clinical and CMC modules, as well as the finalization of the clinical safety section and preparation of interim clinical efficacy data and comparator data for review with FDA, EMA, MHRA and TGA. With OST-400 recruitment now having achieved critical mass, the Company expects to further reduce expenses associated with the Phase 2b clinical program. The Company expects to spend a total of $1 million to open the confirmatory Phase 3 program in Australia, with a significant portion of those expenses having already been spent in the second quarter of 2026.

As a result, the Company reiterates that it has sufficient cash and cash resources, primarily from the LOC, to continue operations into 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 and MHRA. Under the RPDD FDA program, if the Company receives a BLA in the United States, it will become eligible to receive a Priority Review Voucher (PRV) that it intends to sell. The Company is seeking to obtain a BLA under the Accelerated Approval Program for OST-HER2 in osteosarcoma by year-end 2026 in the U.S., in addition to conditional Marketing Authorisation Applications in Europe, the U.K. and Australia.

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 has previously been 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 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 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.

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