OS Therapies Achieves Statistically Significant 2.5-Year Overall Survival in Phase 2b Trial of OST-HER2 in Fully Resected Pulmonary Metastatic Osteosarcoma

Rhea-AI Summary

OS Therapies (NYSE American: OSTX) reported Phase 2b data for OST-HER2 in fully resected pulmonary metastatic osteosarcoma, showing 75% 2.5-year overall survival vs. 47% pooled historical control (p=0.003), with no new deaths since the 2-year analysis (75% vs. 60%, p=0.034).

Updated efficacy and biomarker data are being added to regulatory dossiers as the company pursues early market authorizations in the U.S., U.K., Europe and Australia in late 2026, supported by aligned EMA/TGA use of upcoming 3-year overall survival and a planned confirmatory Phase 3 starting late Q3-2026.

Positive

• 2.5-year overall survival 75% vs. 47% historical control (p=0.003)
• No new patient deaths between 2-year and 2.5-year OST-HER2 timepoints
• EMA and TGA aligned on 3-year overall survival as key efficacy endpoint
• Rolling review underway for conditional Marketing Authorisation in Europe
• BLA filing started under FDA Accelerated Approval Program with Type B meeting planned
• OST-HER2 granted ODD, FTD, RPDD (FDA) and ODD, FTD, ATMP (EMA)
• Potential Priority Review Voucher if BLA granted under RPDD, which company intends to sell
• Confirmatory global Phase 3 trial expected to initiate in late Q3-2026 in Australia

Negative

• None.

News Market Reaction – OSTX

-2.14%

11 alerts

-2.14% Session close to close

+10.7% Peak in 2 hr 38 min

$83.29M Market Cap

0.1x Rel. Volume

In the Jun 2 session, OSTX declined 2.14%, reflecting a moderate negative market reaction. Argus tracked a peak move of +10.7% during that session. Our momentum scanner triggered 11 alerts that day, indicating notable trading interest and price volatility.

Data tracked by StockTitan Argus on the day of publication.

Market Context

This announcement reports statistically significant Phase 2b results, with OST‑HER2 achieving 75% 2....

Analysis

This announcement reports statistically significant Phase 2b results, with OST‑HER2 achieving 75% 2.5‑year overall survival versus 47% historical control (p=0.003) and no new deaths between 2 and 2.5 years. The company is integrating these data into ongoing FDA, EMA, MHRA and TGA discussions, targeting early market authorizations supported by 3‑year overall survival in early Q4‑2026 and a confirmatory Phase 3 starting in late Q3‑2026. Investors may watch upcoming regulatory meetings and Phase 3 readiness closely.

Key Figures

2.5-year OS OST-HER2: 75% 2.5-year OS control: 47% P-value (2.5-year OS): p = 0.003 +5 more

8 metrics

2.5-year OS OST-HER2 75% Phase 2b trial, fully resected pulmonary metastatic osteosarcoma

2.5-year OS control 47% Pooled historical control in Phase 2b comparison

P-value (2.5-year OS) p = 0.003 OST-HER2 vs pooled historical control

2-year OS OST-HER2 75% Earlier Phase 2b timepoint

2-year OS control 60% Pooled historical control at 2 years

P-value (2-year OS) p = 0.034 OST-HER2 vs pooled historical control at 2 years

3-year OS data timing early Q4-2026 Key approvable clinical endpoint for EMA and TGA

Phase 3 initiation late Q3-2026 Confirmatory Phase 3 study start expected in Australia

Historical Context

5 past events · Latest: May 29 (Positive)

Pattern 5 events

Date	Event	Sentiment	24h Move	Catalyst
May 29	Clinical/regulatory update	Positive	+8.1%	Highlighted OST-HER2 OS data and global accelerated approval strategy.
May 26	Conference participation	Positive	+1.2%	Planned sharing of 2.5-year data and investor/partner meetings.
May 18	Q1 2026 earnings	Negative	-8.0%	Reported larger net loss while updating funding and regulatory progress.
May 15	Earnings date notice	Neutral	-8.0%	Announced timing of Q1 2026 financial release and business update.
May 14	Leadership appointment	Positive	+5.0%	Named Dr. Craig Eagle Chief Medical Advisor to advance OST-HER2.

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

Pattern Detected

Recent OSTX news has more often been met with price moves that align with the underlying news tone, with only one notable divergence on a neutral catalyst.

Recent Company History

Across the last several months, OS Therapies has steadily built the OST‑HER2 metastatic osteosarcoma story. On May 14, a positive leadership hire coincided with a price gain. Subsequent earnings on May 18 highlighted larger net losses yet extended cash runway, and regulatory/clinical communication on May 26 and May 29 focused on 2.5‑year survival data and accelerated approvals, generally met with positive reactions. Today’s statistically significant Phase 2b survival update fits this ongoing shift from early data to late-stage regulatory positioning.

Key Terms

overall survival, kaplan-meier, pharmacodynamic, biomarker, +4 more

8 terms

overall survival medical

"75% 2.5-year overall survival for OST-HER2 vs. 47% pooled historical control"

Overall survival is the average or median length of time patients remain alive after starting a treatment or entering a clinical study, measured regardless of cause of death. Investors care because it is a clear, hard measure of a therapy’s real-world benefit — like timing how long a new battery actually runs — and strong improvements in overall survival can drive regulatory approval, market adoption and revenue potential.

kaplan-meier medical

"Figure 1 - Overall Survival Kaplan-Meier Curve"

A Kaplan-Meier estimate is a statistical curve that shows how long it takes for a particular event—such as recovery, relapse, or death—to occur in a group over time, with the curve stepping down as events happen. Investors use these curves to assess the duration and timing of a treatment's or risk's effects—like watching how many light bulbs remain working week by week—because the timing and likelihood of outcomes influence clinical decisions, regulatory approval, and revenue prospects.

pharmacodynamic medical

"supported by a unique, patent pending pharmacodynamic immune response biomarker signature"

Pharmacodynamic describes how a drug acts on the body — the biological effects it produces, how strong those effects are, and how long they last. For investors, pharmacodynamic data show whether a treatment actually works and at what dose, shaping expectations about a drug’s safety, effectiveness, regulatory success and market potential; think of it like testing how well a key turns a lock and whether it reliably opens the door.

biomarker medical

"immune response biomarker signature (Antigen Presentation, NK Cell Activation, T Cell Activation, etc.)"

A biomarker is a measurable indicator found in the body, such as in blood or tissues, that provides information about health, disease, or how the body responds to treatment. For investors, biomarkers can signal the potential success or risk of medical products or therapies, influencing the value of related companies and industry trends. They act like signals or clues that help assess the progress of medical advancements and their market impact.

orphan drug designation regulatory

"OST-HER2 has received Orphan Drug Designation (ODD), Fast Track Designation (FTD)"

Orphan drug designation is a special status given to medicines developed to treat rare diseases affecting only a small number of people. This status often provides benefits like faster approval processes and financial incentives, making it more attractive for companies to develop these drugs. For investors, it signals potential for exclusive market rights and reduced competition, which can impact the drug’s profitability.

fast track designation regulatory

"OST-HER2 has received Orphan Drug Designation (ODD), Fast Track Designation (FTD)"

Fast track designation is a status the U.S. Food and Drug Administration grants to drugs intended to treat serious conditions and address an unmet medical need. It gives the developer more frequent communication with the FDA and can allow parts of the application to be reviewed on a rolling basis, and it may pave the way to priority review or accelerated approval. It can shorten development timelines, though it does not guarantee approval.

rare pediatric disease designation regulatory

"Rare Pediatric Disease Designation (RPDD) from the FDA"

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.

priority review voucher regulatory

"it will become eligible to receive a Priority Review Voucher (PRV) which it intends to sell"

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.

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

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• 75% 2.5-year overall survival for OST-HER2 vs. 47% pooled historical control (p = 0.003), with no new patient deaths reported since the 2-year overall survival data (75% vs. 60%, p = 0.034)
• Updated clinical efficacy data being added to regulatory dossiers as Company seeks early market authorizations in U.S., U.K., Europe and Australia in 2^nd half of 2026
• EMA and Australia TGA (TGA) alignment achieved on early Q4-2026 3-year overall survival data, supported by biomarker data, as key approvable clinical efficacy endpoint
• Upcoming U.S. FDA and U.K. MHRA meetings seek alignment with EMA and TGA on Phase 2b 3-year overall survival and biomarker data to support early market access
• Confirmatory Phase 3 study, required to have commenced prior to grant of early market access in U.S., U.K., Europe or Australia, expected to initiate in late Q3-2026 in Australia

New York and Rockville, Maryland--(Newsfile Corp. - June 2, 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 its Phase 2b trial of OST-HER2 in the prevention or delay of recurrence in fully resected, pulmonary metastatic osteosarcoma (the "Metastatic Osteosarcoma") achieved statistically significant benefit for OST-HER2 treated patients in overall survival at the 2.5-year timepoint (75% vs. 47%, p = 0.003, Figure 1 OST-HER2 vs. pooled historical control). The topline data shows improving OST-HER2 survival benefit when compared with the 2-year data (2-year overall survival was 75% vs. 60%, p = 0.034). No new patient deaths were reported between the 2 and 2.5-year timepoints in the OST-HER2 treated group. OST-HER2 data is supported by a unique, patent pending pharmacodynamic immune response biomarker signature (Antigen Presentation, NK Cell Activation, T Cell Activation, etc.) that was developed as a surrogate clinical efficacy endpoint. The Company intends to present detailed data results during the MIB Agents Factor 2026 Osteosarcoma Conference being held June 25-27, 2026 in Columbus, OH.

"The osteosarcoma community is eagerly awaiting its first approved immunotherapy that has a strong safety profile and activates the immune system to surveil against pulmonary recurrence," said Dr. Peter Anderson, pediatric oncologist at Cleveland Clinic Children's and member of the scientific advisory board for OS Therapies. "New treatments are needed for metastatic osteosarcoma, so I am hopeful OST-HER2 could become an option in the near future."

Figure 1 - Overall Survival Kaplan-Meier Curve 

To view an enhanced version of this graphic, please visit:
https://images.newsfilecorp.com/files/11596/299769_os-therapies.jpg

OS Therapies is now updating its ongoing U.S. and international regulatory market authorization submissions for OST-HER2 in Metastatic Osteosarcoma with this new clinical efficacy data. The European Medicines Agency (EMA) and the Australian Therapeutic Goods Administration (TGA) have already aligned on the use of 3-year overall survival data that will be available in early Q4-2026 as the key clinical efficacy data to support the Company's conditional Marketing Authorisation Applications (cMAAs), with rolling review already underway in Europe. The Company has an upcoming Type B Pre-BLA Meeting with the U.S. Food & Drug Administration (FDA) to gain alignment on use of the forthcoming 3-year overall survival to support a Biologics Licensing Application (BLA) under the Accelerated Approval Program.

"The sustained survival benefit for patients treated with our immunotherapy, with no new deaths reported between the 2-year and 2.5-year timepoints, demonstrates potential durability of OST-HER2's clinical benefit for metastatic osteosarcoma patients," said Dr. Craig Eagle, Chief Medical Advisor of OS Therapies. "As we engage further with regulators on the risk-benefit of OST-HER2 treatment for patients likely to experience metastatic osteosarcoma recurrence, we believe that sustained overall survival benefit, when coupled with the biomarker data, will support early market access authorizations in late 2026. With 3-year survival data on the horizon in early Q4-2026 to support our FDA, EMA, MHRA and TGA filings for early market access, we anticipate receiving authorizations in late Q4-2026."

OS Therapies also has an upcoming Type C Meeting with FDA, and a separate Scientific Advice Meeting (SAM) with the U.K.'s Medicines and Healthcare products Regulatory Agency (MHRA), both being held in early June 2026, to confirm each agency's alignment with the key design parameters already agreed upon with EMA and TGA for the confirmatory Phase 3 protocol.

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) which it intends to sell. The Company has begun filing a BLA for OST-HER2 in pulmonary metastatic osteosarcoma with FDA under the Accelerated Approval Program for OST-HER2 and has received rolling review from the EMA. The Company also anticipates CMA decisions in Europe, the U.K. and Australia in late 2026.

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 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 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 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 expectations regarding cash runway into 2027, 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 because 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 Chen F, et al. Repeat resection of pulmonary metastasis is beneficial for patients with osteosarcoma of the extremities. Interact Cardiovasc Thorac Surg. 2009 Oct;9(4):649-53.
² Carola A.S. Arndt, et al; Inhaled Granulocyte-Macrophage Colony Stimulating Factor for First Pulmonary Recurrence of Osteosarcoma: Effects on Disease-Free Survival and Immunomodulation. A Report From the Children's Oncology Group. Clin Cancer Res 1 August 2010; 16 (15): 4024-4030.
³ Hingorani P, et al. Phase 2 study of anti-disialoganglioside antibody, dinutuximab, in combination with GM-CSF in patients with recurrent osteosarcoma: A report from the Children's Oncology Group. Eur J Cancer. 2022;172:264-275.
⁴ Kempf-Bielack B, et al. Osteosarcoma relapse after combined modality therapy: an analysis of unselected patients in the Cooperative Osteosarcoma Study Group (COSS). J Clin Oncol. 2005;23(3):559-568.
⁵ Janeway KA, et al. A Phase 2 Trial of RANKL Antibody, Denosumab, in Two Cohorts of Patients with Recurrent/Refractory Osteosarcoma, a Report from the Children's Oncology Group. Clin Cancer Res. 2026;32(1):36-44.
⁶ Leary SE, et al. Survival of pediatric patients after relapsed osteosarcoma: the St. Jude Children's Research Hospital experience. Cancer. 2013;119(14):2645-2653.
⁷ Chou AJ, et al. Treatment of osteosarcoma at first recurrence after contemporary therapy: the Memorial Sloan-Kettering Cancer Center experience. Cancer. 2005;104(10):2214-2221.

To view the source version of this press release, please visit https://www.newsfilecorp.com/release/299769

FAQ

What were the key Phase 2b 2.5-year survival results for OST-HER2 in osteosarcoma (OSTX)?

OST-HER2 achieved 75% 2.5-year overall survival versus 47% in a pooled historical control, with p=0.003. According to OS Therapies, no new patient deaths occurred between the 2-year and 2.5-year timepoints, where survival was 75% versus 60% (p=0.034).

How is OS Therapies (OSTX) using OST-HER2 Phase 2b data to seek early market authorization in 2026?

OS Therapies is updating U.S. and international regulatory submissions with the new survival and biomarker data. According to OS Therapies, EMA and TGA have aligned on early Q4-2026 3-year overall survival as the key efficacy endpoint for conditional or early market access decisions in late 2026.

What regulatory designations has OST-HER2 received from the FDA and EMA?

OST-HER2 has received Orphan Drug, Fast Track and Rare Pediatric Disease designations from the FDA, plus ODD, FTD and ATMP status from the EMA. According to OS Therapies, a granted U.S. BLA under RPDD could make the company eligible for a Priority Review Voucher.

When is the confirmatory Phase 3 trial of OST-HER2 expected to start, and where will it begin?

The confirmatory Phase 3 study is expected to initiate in late Q3-2026 in Australia. According to OS Therapies, this trial must have commenced before early market access can be granted in the U.S., U.K., Europe or Australia and is being aligned with EMA and TGA parameters.

What role does the biomarker signature play in the OST-HER2 Phase 2b osteosarcoma trial?

The OST-HER2 data are supported by a unique, patent-pending pharmacodynamic immune response biomarker signature. According to OS Therapies, this signature, reflecting antigen presentation and immune cell activation, was developed as a surrogate clinical efficacy endpoint and will support regulatory evaluations alongside overall survival outcomes.

How might a Priority Review Voucher from OST-HER2 approval impact OS Therapies (OSTX)?

If the OST-HER2 BLA is granted under the Rare Pediatric Disease program, OS Therapies may receive a Priority Review Voucher. According to OS Therapies, the company intends to sell any such voucher, which could provide additional non-dilutive funding if realized.

What regulatory meetings are planned for OST-HER2 in 2026, and why are they important for OSTX investors?

OS Therapies has an upcoming Type B Pre-BLA meeting and Type C meeting with FDA, plus a Scientific Advice Meeting with U.K. MHRA. According to OS Therapies, these aim to align on using 3-year overall survival and Phase 3 design to support potential early market access in late 2026.