New York, NY — December 9, 2025 — OS Therapies announced a successful pre-Marketing Authorisation Application (MAA) meeting with the UK Medicines and Healthcare Products Regulatory Agency (MHRA), achieving alignment on all major components needed for the potential conditional approval of OST-HER2, its listeria-based immunotherapy for preventing or delaying recurrence in fully resected pulmonary metastatic osteosarcoma. The Company confirmed it remains on track to submit its MAA by January 2026, marking a pivotal regulatory moment for this rare and aggressive cancer.
Science Significance
The OST-HER2 program represents a novel immunotherapy approach leveraging listeria-based immune stimulation to target HER2-positive tumor cells, addressing a critical unmet need in metastatic osteosarcoma. OS Therapies advanced compelling biomarker correlations showing that immune activation patterns observed in long-term surviving canine patients align with 2-year overall survival data in human Phase 2b participants. These biomarker signatures are being positioned as a pre-specified surrogate efficacy endpoint, strengthening scientific justification for conditional approval while demonstrating that OST-HER2 may influence disease biology rather than merely delay recurrence.
Regulatory Significance
During the MHRA meeting, OS Therapies achieved agreement on non-clinical requirements, CMC (chemistry, manufacturing, and controls) expectations, and post-market confirmatory study design, enabling a clear regulatory pathway toward conditional MAA submission. Importantly, MHRA acknowledged the relevance of the proposed biomarker-based surrogate endpoint, pending final analytical alignment with the U.S. FDA, to be discussed in a Type C Meeting on December 11, 2025. This cross-agency coordination supports future Biologics License Application (BLA) plans under the FDA’s Accelerated Approval Program, further solidifying OST-HER2’s regulatory momentum across major jurisdictions.
Business Significance
Advertisement
For OS Therapies, the successful MHRA interaction reinforces investor confidence and affirms the Company’s position as a global leader in listeria-based cancer immunotherapies. OST-HER2 has already demonstrated statistically significant benefit in 12-month event-free survival in its Phase 2b trial, strengthening the commercial case for a first-in-class therapy in a rare pediatric-priority market. With anticipated BLA submission in early 2026 and eligibility for a Priority Review Voucher, the program carries substantial long-term value potential. OS Therapies is simultaneously advancing a next-generation tunable ADC (tADC) platform, further expanding its oncology pipeline and enhancing strategic business resilience.
Patients’ Significance
Metastatic osteosarcoma—particularly cases involving fully resected pulmonary metastases—remains one of the most challenging pediatric and adolescent cancers, with limited treatment options and high recurrence risk. OST-HER2 has demonstrated encouraging long-term survival potential and a favorable immunologic response profile, offering hope for improved outcomes where no approved therapies currently exist. A conditional MAA, if granted, would represent one of the most significant therapeutic advances for this rare cancer in decades, providing families with access to a therapy designed to prevent or meaningfully delay relapse, a key determinant of survival.
Policy Significance
The coordinated regulatory engagement between MHRA and FDA highlights the growing importance of innovative approval pathways for rare pediatric diseases. OST-HER2 has received Rare Pediatric Disease, Fast-Track, and Orphan Drug designations, underscoring policy priorities to accelerate therapies in areas of high unmet need. As regulatory agencies increasingly accept surrogate endpoints and biomarker-driven evidence, this program may help shape future frameworks governing conditional approvals, post-market commitments, and cross-border harmonization for rare-disease oncology therapeutics.
OS Therapies’ successful MHRA pre-MAA meeting marks a defining step toward bringing OST-HER2 to patients with recurrent metastatic osteosarcoma, a population with starkly limited treatment options. With regulatory momentum building in both the UK and U.S., and with strong scientific and clinical foundations, the Company is positioned to potentially deliver the first approved immunotherapy specifically targeting recurrence prevention in this devastating cancer. As OS Therapies advances toward its January 2026 MAA submission, the global oncology community will be watching closely as this breakthrough therapy moves toward regulatory review and, ultimately, patient access.
Source: OS Therapies Inc. press release
