OS Therapies Announces EMA Initiates Rolling Review of Conditional Marketing Authorization Application for OST-HER2 in the Prevention or Delay of Recurrence in Fully Resected Pulmonary Metastatic Osteosarcoma

Rhea-AI Summary

OS Therapies (NYSE: OSTX) announced that the EMA has initiated a rolling review of OST-HER2 for prevention of recurrence in fully resected pulmonary metastatic osteosarcoma and selected the company for EMA's Raw Data Pilot.

EMA, Australian TGA and UK MHRA/ATGA aligned on 3-year overall survival as the approvable efficacy endpoint and on seroconversion as a surrogate; Phase 3 initiation is planned in Australia in Q3 2026. OST-HER2 holds multiple orphan/accelerated designations and the company forecasts >$300M peak European sales and >$50M in 2027.

Positive

• EMA initiated rolling review of OST-HER2 CMA request
• OST-HER2 received ATMP designation from UK MHRA
• Regulatory alignment on 3-year overall survival primary endpoint and seroconversion surrogate
• Planned Phase 3 start in Q3 2026 (Australia) to support early approvals
• Company forecasts > $300M peak European sales and $50M+ in 2027

Negative

• Early market access requires initiation of a confirmatory Phase 3 trial prior to approval
• EMA requested updated 2.5-year and 3-year overall survival data, extending key submission timelines

News Market Reaction – OSTX

+4.29%

17 alerts

+4.29% Session close to close

+9.2% Peak Tracked

-8.0% Trough Tracked

$79.87M Market Cap

0.6x Rel. Volume

In the Apr 30 session, OSTX gained 4.29%, reflecting a moderate positive market reaction. Argus tracked a peak move of +9.2% during that session. Argus tracked a trough of -8.0% from its starting point during tracking. Our momentum scanner triggered 17 alerts that day, indicating notable trading interest and price volatility.

Data tracked by StockTitan Argus on the day of publication.

Market Context

This announcement details EMA rolling review for OST-HER2, alignment on 3-year overall survival as t...

Analysis

This announcement details EMA rolling review for OST-HER2, alignment on 3-year overall survival as the primary endpoint, and coordinated plans for Conditional Marketing Authorizations and a U.S. Accelerated Approval BLA. It also highlights ATMP status, projected European peak sales above $300 million, and platform expansion into prostate, lung and pancreatic cancers. Investors may track upcoming survival data updates, Phase 3 initiation in Q3 2026, and the planned 2027 launch expectations.

Key Figures

Overall survival endpoint: 3-year overall survival Overall survival data: 2-year overall survival Updated survival data: 2.5-year overall survival +5 more

8 metrics

Overall survival endpoint 3-year overall survival Primary clinical efficacy endpoint for confirmatory Phase 3 and CMA evaluation

Overall survival data 2-year overall survival Submitted efficacy data supporting EMA rolling review

Updated survival data 2.5-year overall survival Requested by EMA, expected mid Q2 2026

Forecast peak sales over $300 million Company forecast for European OST-HER2 osteosarcoma sales after ATMP designation

Initial 2027 sales over $50 million Company forecast for OST-HER2 European sales in 2027

VAT refund approximately 1.45 million GBP Expected non-dilutive cash VAT tax refund

KRAS mutation coverage 76% of all KRAS mutations KRAS G12 position mutations targeted by OST-503

Phase 3 start timing Q3 2026 Planned initiation of confirmatory Phase 3 osteosarcoma trial in Australia

Historical Context

5 past events · Latest: Apr 27 (Positive)

Pattern 5 events

Date	Event	Sentiment	24h Move	Catalyst
Apr 27	Biomarker call scheduled	Positive	-7.9%	Announced OST-HER2 biomarker conference call and reiterated accelerated approval plans.
Apr 16	Biomarker patent filing	Positive	+1.4%	Filed patent on immune signature biomarker supporting OST-HER2 regulatory strategy.
Apr 13	Strategic advisor hire	Positive	+1.5%	Appointed Robert Langer as strategic advisor to guide oncology pipeline.
Apr 8	Strategic advisor hire	Positive	+1.6%	Added Craig Eagle to advisory board to support osteosarcoma regulatory execution.
Apr 2	Registered direct offering	Negative	-6.6%	Completed $5.25M registered direct equity financing at $1.40 per share.

24h Move is the share-price change in the day after each event; other market factors may also have contributed.

Pattern Detected

OSTX usually trades in line with news tone: positive strategic or regulatory updates have mostly seen positive price reactions, while financing news and one recent biomarker call drew selling pressure.

Recent Company History

Over the last month, OS Therapies has focused on OST-HER2 regulatory and strategic positioning, including board-level advisory appointments and biomarker-driven conference calls. A $5.25M registered direct offering on Apr 2, 2026 weighed on the stock, but later news about patent filings and high-profile advisors saw modest gains. Today’s EMA rolling review and multi-agency alignment extend this regulatory narrative, building on the Accelerated Approval and CMA roadmap highlighted in prior updates.

Key Terms

conditional marketing authorisation, rolling review, advanced therapy medicinal product, priority review voucher, +4 more

8 terms

conditional marketing authorisation regulatory

"OST-HER2 Conditional Marketing Authorisation (CMA) request regulatory dossier"

A conditional marketing authorisation is a regulator’s temporary approval allowing a medicine or vaccine to be sold before all long-term data are available because early evidence suggests its benefits outweigh the risks; the company must complete further studies or meet other requirements afterward. Think of it like a provisional driver’s license that lets a product start earning revenue sooner but carries obligations and the risk of restrictions or withdrawal if follow-up data are unsatisfactory, which makes it important for investors weighing near-term sales versus regulatory and clinical risk.

rolling review regulatory

"has initiated Continuous Evaluation ("Rolling Review") of the OST-HER2"

A rolling review is a regulatory process where health authorities examine data on a drug or vaccine as it becomes available instead of waiting for a complete file at the end. For investors, this can speed up the timeline to approval and reduce uncertainty because regulators assess progress in real time—think of reading and approving chapters of a book as they’re finished rather than waiting for the whole manuscript, which can bring forward potential market access and revenue.

advanced therapy medicinal product regulatory

"been granted Advanced Therapy Medicinal Product designation from the U.K."

Medicines made from living cells, genes, or engineered tissues that aim to treat or cure disease by changing biological processes rather than using traditional chemical drugs. They matter to investors because they can command high prices and rapid growth if approved, but also carry large development costs, complex manufacturing and regulatory hurdles, and binary outcomes (success or failure) that can dramatically affect a company’s value—think of them as high-risk, high-reward bespoke therapies.

priority review voucher regulatory

"eligibility for a Priority Review Voucher (PRV) under Rare Pediatric"

A priority review voucher is a transferable regulatory incentive that lets a company move a future drug or device application to the front of the review line, shortening the review period by several months. For investors it matters because the voucher can speed up market access for a high-value product or be sold to other companies for significant cash, acting like a tradable fast-pass that can accelerate revenue or create immediate financial upside.

rare pediatric disease designation regulatory

"Voucher (PRV) under Rare Pediatric Disease Designation (RPDD)"

A rare pediatric disease designation is an official regulatory status given to a drug or therapy that targets a serious or life‑threatening condition primarily affecting children and is uncommon in the population. It matters to investors because the status often brings financial and development perks — such as tax credits, reduced fees, faster review and periods of market protection — which can lower costs, speed approval and improve the commercial outlook; think of it as a VIP pass that makes bringing a scarce, child‑focused treatment to market easier and potentially more profitable.

biologics license application regulatory

"as well as a U.S. Biologics License Application (BLA) under Accelerated"

A biologics license application is a formal request submitted to regulatory authorities seeking approval to market a new biological medicine, such as vaccines or treatments made from living organisms. It is a comprehensive review process that evaluates the safety, effectiveness, and manufacturing quality of the product. For investors, receiving approval signals that a biological therapy can be sold to the public, potentially leading to revenue growth and market success.

accelerated approval regulatory

"obtain a BLA under the Accelerated Approval Program for OST-HER2"

Accelerated approval is a process that allows new medical treatments to be approved more quickly than usual if they address serious or life-threatening conditions and show promising early results. For investors, it signals that a treatment may reach the market sooner, potentially boosting a company's prospects, but it also involves some uncertainty since full evidence of effectiveness is still being gathered.

listeria monocytogenes medical

"rest of our attenuated listeria monocytogenes platform candidates."

A bacterium that can cause severe foodborne illness, especially dangerous to pregnant people, the elderly and those with weak immune systems. Think of it as a tiny contaminant that can hide in food facilities or packaged products and prompt recalls, regulatory action and lawsuits; for investors, outbreaks can cut sales, raise costs and damage brand value, making it a material operational and reputational risk for food-related companies.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Conference call scheduled for Thursday, April 30, 2026, at 8:30 am ET to review new OST-HER2 immune pharmacodynamic biomarker response (seroconversion) data and review regulatory successes validating the OST-HER2 approach. Participants will include strategic advisors Dr. Craig Eagle and Dr. Bob Langer, and Osteosarcoma key opinion leader Dr. Peter Anderson from Cleveland Clinic.

• EMA and Australia TGA (ATGA) align on 3-year overall survival as the approvable clinical efficacy endpoint for Conditional Marketing Authorizations (CMAs), with alignment also achieved on confirmatory Phase 3 initiation, initially only in Australia, planned for Q3 2026 to meet regulatory requirement to support early approvals in the U.S., U.K., Europe and Australia
• Alignment achieved with EMA and ATGA on Seroconversion data serving as surrogate clinical efficacy data to support CMAs for early market access and eligibility for a Priority Review Voucher (PRV) under Rare Pediatric Disease Designation (RPDD)
• Alignment achieved with EMA and ATGA on non-clinical, CMC and safety data
• Alignment achieved with ATGA on existing drug product being used to initiate Phase 3
• EMA selects Company into Raw Data Pilot Program
• OST-HER2 granted ATMP designation by U.K. MHRA
• Company forecasts European peak OST-HER2 osteosarcoma sales exceeding $300 million following ATMP designation grant, with over $50 million in sales expected in 2027
• Upcoming U.S. FDA and U.K MHRA meetings scheduled in 2nd quarter of 2026
• OST-504 Phase 1b castrate resistant prostate cancer trial biomarker analysis to mirror OST-HER2 Phase 2b osteosarcoma biomarker analysis
• OST-503 Phase 2 non-small cell lung cancer candidate indications expanded to include pancreatic cancer following review of target vector antigens include all KRAS G12 position mutations, which represents 76% of all KRAS mutations in cancer

New York, New York--(Newsfile Corp. - April 30, 2026) - OS Therapies, Inc. (NYSE American: OSTX) ("OS Therapies" or "the Company"), the world leader in gene-edited, listeria-based cancer immunotherapies, today announced that the European Medicines Agency (EMA)'s Committee for Advanced Therapy (CAT), in conjunction with the Committee for Medicinal Products for Human Use (CHMP) and Pharmacovigilance Risk Assessment Committee (PRAC), has initiated Continuous Evaluation ("Rolling Review") of the OST-HER2 Conditional Marketing Authorisation (CMA) request regulatory dossier for the prevention of recurrence in fully resected, pulmonary metastatic osteosarcoma.¹ The Company also announced that it was selected into EMA's Raw Data Pilot programme.

Concurrent with this announcement, the This effort will be done in concert with the EMA Scientific Advice Working Party (SAWP). TGA has also invited the OS Therapies to make an application for Provisional Determination, the Australian equivalent of a Conditional Marketing Authorisation of the OST-HER2 regulatory dossier, and is expected to make a decision on rolling review following the receipt of the Clinical Trial Notification (CTN) for the confirmatory Phase 3 trial later this quarter that will position the OS Therapies to initiate the confirmatory Phase 3 in the third quarter of 2026.

"I am delighted with the regulatory interactions OS Therapies has had to date, and I look forward to supporting OS Therapies in upcoming meetings with U.S. and U.K regulators," said Dr. Craig Eagle, strategic advisor for OS Therapies.

OST-HER2 Immune Pharmacodynamic Biomarkers Conference Call Details

Title: OS Therapies (NYSE: OSTX) | Conference Call: OST-HER2 immune pharmacodynamic response biomarkers
Date: April 30^th, 2026
Time: 8:30 AM Eastern Time
Registration Link: https://zoom.us/webinar/register/WN_Xlmj7kdNTH6C0MA_xdwiiQ

EMA OST-HER2 Rolling Review Status

OS Therapies and EMA have agreed that 3-year overall survival data will serve as the basis to complete evaluation of the CMA request. The Company's recently submitted clinical efficacy data includes 2-year overall survival data, with EMA requesting updated 2.5-year overall survival data that will be available by the middle of the second quarter of 2026, and 3-year overall survival data that will become available early in the fourth quarter of 2026, which will complete the CMA submission. The Company anticipates a potential CMA decision by EMA in the fourth quarter of 2026. Market access interactions related to reimbursement with the UK's NICE and EMA Health Technology Assessment (HTA) processes have commenced simultaneously to minimize the time between regulatory approval(s) and patient access to treatment. International regulatory coordination has also commenced under the EMA FDA Information Sharing programme².

Additionally, the Company has been granted Advanced Therapy Medicinal Product designation from the U.K. Medicines and Healthcare products Regulatory Agency (MHRA)³ by virtue of its reciprocal designation agreement with EMA.

"We are grateful for EMA and ATGA's strong support of our OST-HER2 program as we urgently work to improve outcomes for patients facing this rare and deadly pediatric cancer," said Paul Romness, Chair and Chief Executive Officer of OS Therapies. "With all currently available data submitted and key regulatory alignment achieved, we are advancing toward early market access via Conditional Marketing Authorizations in Europe, the U.K., and Australia, as well as a U.S. Biologics License Application (BLA) under Accelerated Approval. Following our recent ATMP designation in Europe, we believe peak European sales could exceed $300 million annually, with the potential to generate more than $50 million in sales beginning in 2027." Mr. Romness continued: "We have aligned with EMA and ATGA on the provisional design of our global confirmatory Phase 3 trial that is required to be initiated prior to being granted early market access, including 3-year overall survival as the primary efficacy endpoint. 3-year overall survival will also be the efficacy endpoint that will serve as the basis for potential early market access in the U.S., U.K., Europe, and Australia. This gives us strong confidence as we head into upcoming FDA and MHRA meetings, while reinforcing the growing recognition of our pharmacodynamic biomarker response seroconversion data as a meaningful surrogate for the key overall survival efficacy endpoint, further supporting our global regulatory pathway. We are delighted that immunotherapies are becoming more central in the approach to treating cancers globally, which bolsters OST-HER2 and the rest of our attenuated listeria monocytogenes platform candidates."

"With the significant momentum we now have surrounding OST-HER2 in osteosarcoma, we are actively working to be prepared for the time when resources become available to advance our exciting listeria monocytogenes platform pipeline," said Robert Petit, PhD, Chief Medical and Scientific Officer at OS Therapies. "Based upon the extensive biomarker work we have done to date on the OST-HER2 osteosarcoma program, we are now positioned to generate congruent data for the OST-504 castration-resistant prostate cancer program. Additionally, following significant advancement in the exciting KRAS-targeted antibody pancreatic cancer field with important clinical data showing significant survival benefit, we have identified that our promising Phase 2 non-small cell lung cancer (NSCLC) candidate OST-503 was constructed to target all KRAS G12 position-related antigen mutations, which represents 76% of all KRAS mutations in cancer. As a result, we believe OST-503 could represent a highly complementary approach to KRAS-target antibodies currently in development."

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 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 in the second half of 2026, in addition to CMAs in Europe, the U.K. and Australia.

Upcoming 2^nd Quarter Milestones

• 2.5-year overall survival data
• FDA Pre-BLA Type B meeting to gain alignment on surrogate clinical efficacy endpoints based on most up-to-date Phase 2b clinical, biomarker and CMC, following the December 2025 alignment achieved non-clinical and safety data
• Regenerative Medicine Advanced Therapy designation ("RMAT" - FDA equivalent to EMA ATMP designation) decision to be based upon preliminary evidence of efficacy supported by clinical and biomarker data metrics aligned upon
• FDA rolling review decision based upon pre-BLA meeting outcome
• FDA Type C meeting to gain alignment on the design of the confirmatory Phase 3 study
• Submission of the Accelerated Approval BLA request to FDA
• MHRA meeting to gain alignment on the design of the confirmatory Phase 3 study
• Submission of CMA request to MHRA
• MHRA rolling review decision based on Phase 3 confirmatory study design alignment
• Submission of CMA request to Australia in conjunction with Clinical Trial Notification (CTN) request for confirmatory Phase 3 study
• Receipt of approximately 1.45 million GBP in non-dilutive cash VAT tax refund

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 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 ATMP from the European Medicines Agency.

The Company reported positive data in its Phase 2b clinical trial of OST-HER2 in recurrent, fully resected, lung 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 anticipates receiving 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 Authorisations 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 been conditionally approved by the U.S. Department of Agriculture for the treatment of canines with osteosarcoma. The Company also anticipates reading out data from a Phase 1b study of OST-504 in castration resistant prostate cancer in the first half of 2026.

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 our expected to provide cash runway into 2027, the intended use of net proceeds from the offering, 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.

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/ 

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¹ https://www.ema.europa.eu/en/about-us/how-we-work/data-regulation-big-data-other-sources/use-clinical-study-data-medicine-evaluation
² https://www.fda.gov/drugs/cder-international-program/international-agreements-information-sharing
³ https://www.gov.uk/guidance/advanced-therapy-medicinal-products-regulation-and-licensing

To view the source version of this press release, please visit https://www.newsfilecorp.com/release/295127

FAQ

What does EMA's rolling review for OST-HER2 (OSTX) mean for approval timing?

Rolling review allows staggered dossier evaluation to potentially speed review. According to OS Therapies, a CMA decision could occur in Q4 2026, contingent on receipt of updated 2.5- and 3-year overall survival data and Phase 3 alignment.

Will OST-HER2 (OSTX) need a Phase 3 trial before early market access?

Yes. According to OS Therapies, initiation of a confirmatory Phase 3 trial is required prior to granting early market access and will begin in Australia in Q3 2026 to support CMAs.

What regulatory designations does OST-HER2 (OSTX) hold that could affect market value?

OST-HER2 holds orphan drug, Fast Track and Rare Pediatric Disease designations from FDA plus ATMP/ATMP-equivalent designations from EMA/MHRA. According to OS Therapies, RPDD eligibility could yield a Priority Review Voucher if a U.S. BLA is granted.

How did EMA and Australia TGA align on surrogate endpoints for OST-HER2 (OSTX)?

They agreed seroconversion biomarker data may serve as a surrogate to support CMAs. According to OS Therapies, this alignment complements 3-year overall survival as the primary efficacy endpoint for approvals.

What commercial expectations did OS Therapies (OSTX) announce for OST-HER2 in Europe?

The company forecasts European peak OST-HER2 sales exceeding $300 million and expects over $50 million in sales in 2027. According to OS Therapies, that projection follows ATMP designation and market-access planning.