On April 10, 2025 OS Therapies (NYSE-A: OSTX) ("OS Therapies" or "the Company"), a clinical-stage immunotherapy and Antibody Drug Conjugate (ADC) biopharmaceutical company, reported positive data in the prevention or delay of amputation during the treatment of primary osteosarcoma for OST-HER2 combined palliative radiation in dogs with unresected appendicular osteosarcoma (Press release, OS Therapies, APR 10, 2025, View Source [SID1234651879]). The treatment led to clinical and radiographic arrest of the primary tumor and prolonged time to metastasis in dogs without surgery or chemotherapy. The data opens the potential for OST-HER2 to be used in frontline therapy in human osteosarcoma prior to initiation of chemotherapy, and potentially reduce the need for chemotherapy altogether, for the purposes of preventing or delaying limb amputation or primary tumor resection surgeries, in addition to the prevention, delay and/or control of lung metastasis.

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Additionally, the Company announced the publication of positive data in the journal "Molecular Therapy" entitled "Immunological responses and clinical outcomes in dogs with osteosarcoma receiving standard therapy and a Listeria vaccine expressing HER2" demonstrated the correlation of innate and adaptive immune responses to OST-HER2, with prevention of metastasis and long-term survival benefit when used in the adjuvant setting, following standard of care amputation and chemotherapy.

Treatment with OST-HER2 was found to be safe and well tolerated in both studies. Taken together, the data support the potential of OST-HER2 to achieve progression free survival (PFS) of primary osteosarcoma, prevent or delay or metastatic disease, prolong progression free survival (PFS) in metastatic disease, and significantly improve long term survival in patients with osteosarcoma. The data on the use of OST-HER2 in unresected primary osteosarcoma in dogs is being prepared for peer-reviewed publication.

"We first published strong clinical data on the benefit of OST-HER2 in canine osteosarcoma in 2016, and that led to an initial conditional approval based on a prior manufacturing process that was suboptimal for widespread veterinary use," said Dr. Nicola Mason, the Paul A. James and Charles A. Gilmore Endowed Professor at the University of Pennsylvania, School of Veterinary Medical. "Based upon this initial research, OS Therapies conducted a successful translational Phase 2b clinical trial in the rare pediatric indication of prevention of recurrence of fully resected, osteosarcoma lung metastases. Our newly published canine data and unpublished radiation combination canine data expands the potential use of OST-HER2 into delay/prevention of metastasis and PFS following resected primary osteosarcoma and raises the intriguing possibility of combination radiation therapy and OST-HER2 in the treatment of unresectable osteosarcoma."

The Company is preparing to submit this data to USDA, along with new data generated on its newly patented, commercially superior manufacturing process, with the aim of gaining conditional approval for the new manufacturing process for OST-HER2 in the United States to begin sales in 2025. Thereafter, the Company intends to conduct a pivotal clinical study with the aim of gaining full approval in 2026. A link to the publication is available here: View Source(25)00113-3.

"It has been my dream since founding the Company that OST-HER2 could potentially change the standard of care in osteosarcoma, potentially limiting the need for amputation or surgical resection of the primary tumor," said Paul Romness, CEO of OS Therapies. "With today’s data, we believe we are taking the first steps towards this given that our Comparative Oncology approach, as a result of the 96% genetic homology between human and canine osteosarcoma, leads us to believe there is significant potential for this canine data to translate into humans in the treatment of frontline and primary metastatic osteosarcoma, similarly to how it has in recurrent, fully-resected, lung metastatic osteosarcoma."

Mr. Romness continued, "We are laser focused on getting an Accelerated Approval for OST-HER2 in recurrent, fully resected, lung metastatic human osteosarcoma via Accelerated Approval by year-end 2025 and then using funds obtained from the sale of our pending Priority Review Voucher to expand the potential clinical uses of OST-HER2 throughout the human osteosarcoma treatment paradigm. In parallel, we believe the data from these two studies support the use of OST-HER2 in all phases of canine osteosarcoma treatment and we are hopeful to obtain conditional approval with our newly improved, patented manufacturing for OST-HER2 later this year so that we can launch the product at specialized cancer centers and our four-legged patients can begin getting treatment very soon.