Overall survival data 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 71.2%, compared with 45.8% of patients in the comparable combined historical control group (p = 0.002, 41 total enrolled patients, with visits for the two remaining patients who have not reached 3-years from enrollment scheduled for September 2026 and early October 2026, respectively, and 6 patients lost to follow-up).

"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 $3.15 million in Value Added Tax (VAT) refunds into its wholly-owned subsidiary OS Therapies UK, Ltd. that also now confirms its eligibility to receive at least an additional $7.2 million in VAT and R&D Tax Credits. Those funds are earmarked for the initiation of the confirmatory Phase 3 clinical trial that is set to commence in the U.K. in order for the Company to become eligible to be granted a BLA under the Accelerated Approval Program in the U.S., as well as Conditional Marketing Authorization Applications (CMAAs) in the U.K., Europe and Australia.

"Following receipt of the first $3.15 million VAT refund through OS Therapies UK, Ltd, we now have resources earmarked to fund the commencement of the confirmatory Metastatic Osteosarcoma Program Phase 3 trial that is required to be initiated prior to an FDA decision on a BLA under the Accelerated Approval Program, as well as MHRA, EMA and TGA decisions on CMAAs," said Paul Romness, MPH, Chair and CEO of OS Therapies. "The opening of that confirmatory trial following the upcoming MHRA meeting will initially be limited to the U.K. because of MHRA allowing the Company to use existing Phase 2 drug product to open that confirmatory Phase 3 trial. Based upon the positive VAT outcome, we have now confirmed our refundable research & development tax credits (Refundable R&D Tax Credits) eligibility and expect a decision on our outstanding $7.2 million refund requests. With our U.K. tax strategy now firmly in place, we expect those funds to fully support the commencement of the U.K. portion of the Phase 3 trial while we wait for early market access regulatory decisions from FDA MHRA, EMA and TGA."

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 $220 million. However, there can be no assurance that the Company would realize a comparable value, if any, in connection with any future PRV sale. OS Therapies has completed resubmission of a Regenerative Medicine Advanced Therapy (RMAT) request and the Company's Commissioner's National Priority Review Voucher (CNPV) letter of intent has been accepted by FDA. The Company intends to request Rolling Review of the ongoing BLA submission that began in January 2026 following its upcoming mid-September 2026 FDA Type C Statistical Methods Meeting. OS Therapies is seeking to obtain a BLA under the Accelerated Approval Program in the U.S. 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.