UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

(Mark One)

☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the fiscal year ended December 31, 2025.

☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from _______ to _______.

Commission file number: 001-42195

OS THERAPIES INCORPORATED

(Exact name of registrant as specified in its charter)

Delaware		82-5118368
(State or other jurisdiction of		(IRS Employer
incorporation or organization)		Identification No.)

115 Pullman Crossing Road, Suite 103 Grasonville, Maryland		21638
(Address of principal executive offices)		(Zip Code)

(410) 297-7793

(Registrant’s telephone number, including area code)

Securities registered pursuant to Section 12(b) of the Act:

Title of each class		Trading Symbol(s)		Name of each exchange on which registered
Common Stock, par value $0.001 per share		OSTX		NYSE American

Securities registered pursuant to Section 12(g) of the Act: None

Indicate by checkmark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes ☐ No ☒

Indicate by checkmark if the registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act. Yes ☐ No ☒

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ☒ No ☐

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files). Yes ☒ No ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer”, “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer	☐	Accelerated filer	☐
Non-accelerated filer	☒	Smaller reporting company	☒
		Emerging growth Company	☒

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm that prepared or issued its audit report. ☐

If securities are registered pursuant to Section 12(b) of the Act, indicate by check mark whether the financial statements of the registrant included in the filing reflect the correction of an error to previously issued financial statements. ☐

Indicate by check mark whether any of those error corrections are restatements that required a recovery analysis of incentive-based compensation received by any of the registrant’s executive officers during the relevant recovery period pursuant to § 240.10D-1(b). ☐

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes ☐ No ☒

The aggregate market value of the registrant’s common stock held by non-affiliates, computed by reference to the price at which the common stock was last sold as of June 30, 2025, the last business day of the registrant’s most recently completed second fiscal quarter, was approximately $49.6 million.

The number of shares of the registrant’s Common Stock outstanding as of March 26, 2026 was 39,533,227 shares.

DOCUMENTS INCORPORATED BY REFERENCE

None.

OS THERAPIES INCORPORATED

TABLE OF CONTENTS

		Page

PART I.		1
Item 1.	Business	2
Item 1A.	Risk Factors	19
Item 1B.	Unresolved Staff Comments	56
Item 1C.	Cybersecurity	56
Item 2.	Properties	56
Item 3.	Legal Proceedings	56
Item 4.	Mine Safety Disclosures	56

PART II.		57
Item 5.	Market for Registrant’s Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities	57
Item 6.	Reserved	57
Item 7.	Management’s Discussion and Analysis of Financial Condition and Results of Operations	58
Item 7A.	Quantitative and Qualitative Disclosures About Market Risk	68
Item 8.	Financial Statement and Supplementary Data	69
Item 9.	Changes in and Disagreements with Accountants on Accounting and Financial Disclosure	104
Item 9A.	Controls and Procedures	104
Item 9B.	Other Information	104
Item 9C.	Disclosure Regarding Foreign Jurisdictions that Prevent Inspections	104

PART III.		105
Item 10.	Directors, Executive Officers and Corporate Governance	105
Item 11.	Executive Compensation	109
Item 12.	Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters	114
Item 13.	Certain Relationships and Related Transactions, and Director Independence	116
Item 14.	Principal Accounting Fees and Services	118

PART IV.		119
Item 15.	Exhibits and Financial Statement Schedules	119
Item 16.	Form 10-K Summary	120

PART I

Cautionary Note Regarding Forward-Looking Statements

This report contains “forward-looking statements” (within the meaning of Section 27A of the Securities Act of 1933, as amended (the “Securities Act”), and Section 21E of the Securities Exchange Act of 1934, as amended (the “Exchange Act”)), which may include information concerning our beliefs, plans, objectives, goals, expectations, strategies, anticipations, assumptions, estimates, intentions, future events, future revenues or performance, capital expenditures and other information that is not historical information. Forward-looking statements involve known and unknown risks, uncertainties and other factors, which may be beyond our control, and which may cause our actual results, performance or achievements to be materially different from future results, performance or achievements expressed or implied by such forward-looking statements. When used in this report, the words “seek,” “estimate,” “expect,” “anticipate,” “project,” “plan,” “contemplate,” “plan,” “continue,” “intend,” “believe” and variations of such words or similar expressions are intended to identify forward-looking statements. All forward-looking statements are based upon our current expectations and various assumptions. We believe there is a reasonable basis for our expectations and beliefs, but there can be no assurance that we will realize our expectations or that our beliefs will prove to be correct.

There are a number of risks and uncertainties that could cause our actual results to differ materially from the forward-looking statements contained in this report. Examples of risks and uncertainties that could cause actual results to differ materially from historical performance and any forward-looking statements include, but are not limited to, the risks described under the section below titled “Risk Factors” of this Form 10-K, as well as any of our subsequent filings with the SEC.

There may be other factors of which we are currently unaware or which we currently deem immaterial that may cause our actual results to differ materially from the forward-looking statements. All forward-looking statements attributable to us or persons acting on our behalf apply only as of the date they are made and are expressly qualified in their entirety by the cautionary statements included in this report. Except as may be required by law, we undertake no obligation to publicly update or revise any forward-looking statement to reflect events or circumstances occurring after the date they were made or to reflect the occurrence of unanticipated events, or otherwise.

We make available through our Internet website, free of charge, our Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q, Current Reports on Form 8-K, and amendments to such reports and other filings made by us with the Securities and Exchange Commission (“SEC”), as soon as practicable after we electronically file such reports and filings with the SEC. Our website address is www.ostherapies.com. The information contained on our website is not incorporated by reference into this report.

Note Regarding Intellectual Property

SiLinkers™, CAPs™ and other common law trade names, trademarks or service marks of our company appearing in this report are the property of OS Therapies Incorporated. This report contains additional trade names, trademarks and service marks owned by their respective owners. Solely for convenience, trademarks and trade names referred to in this annual report may appear without the ™ or ® symbols, but such an omission is not intended to indicate that we will not assert, to the fullest extent under applicable law, our rights, or that the applicable owners will not assert their rights, to these trademarks and trade names. We do not intend our use or display of other companies’ trade names, trademarks or service marks to imply a relationship with, or endorsement or sponsorship by us of, these other companies.

Item 1. Business.

Overview and Mission

OS Therapies Incorporated (“OS Therapies,” the “Company,” “we,” “our” or “us”) is a clinical stage biopharmaceutical company focused on the identification, development and commercialization of treatments for Osteosarcoma (OS) and other solid tumors. Our mission is to address the significant need for new treatments in cancers of the bone in children and young adults. Osteosarcoma is an extremely challenging and often aggressive cancer that has particular treatment challenges due to its location, changing genotypes and high metastases rates. We are currently seeking to answer the call for new treatments that will prevent metastasis and the recurrence of metastases with our lead core product candidate OST-HER2 (also known as OST31-164), a cancer immunotherapy product candidate that produces a cellular immune response against the cancer antigen HER2.

In 2021, we opened a clinical study to produce data for the U.S. Food and Drug Administration (FDA) to evaluate the safety and efficacy of OST-HER2 in patients after resection of recurrent Osteosarcoma, which achieved full enrollment of 41 patients in October 2023. In the first quarter of 2025, we announced that our Phase IIb clinical trial achieved its primary endpoint with statistical significance. In October 2025, we announced final two-year overall survival data from the Phase IIb trial, in which 75% (27 of 36 evaluable patients) of OST-HER2-treated patients achieved two-year overall survival from the most recent pulmonary resection, compared with 40% in historical control patients (p < 0.0001). OST-HER2 was observed to be well-tolerated in the study. In January 2026, we announced positive immune biomarker data from the Phase IIb trial indicating that activation of immune blood biomarkers in the interferon gamma pathway correlated with, and was predictive of, overall survival, distinguishing long-term survivors (≥ two years) from short-term survivors (< one year). These biomarker findings are based on exploratory analyses and have not been validated as surrogate endpoints for clinical benefit. Based on the totality of the data generated to date, including the observed survival outcomes, safety profile and the significant unmet medical need in this patient population, we intend to engage with the FDA regarding potential regulatory pathways for OST-HER2.

We have engaged in ongoing regulatory interactions with the FDA, the United Kingdom Medicines and Healthcare products Regulatory Agency (MHRA), and the European Medicines Agency (EMA) regarding the clinical and biomarker data for OST-HER2 in recurrent, fully resected pulmonary metastatic Osteosarcoma. Following submission of the Non-Clinical and Chemistry, Manufacturing & Controls (CMC) modules of our Biologics License Application (BLA) to the FDA at the end of January 2026, we anticipate submitting the clinical BLA module following an expected Type B meeting with the FDA in the second quarter of 2026 and completing conditional Marketing Authorization Application (MAA) submissions to both the MHRA and the EMA in the second quarter of 2026. We also anticipate releasing additional biomarker data in the second quarter of 2026 to further characterize immune pathway activation and its relationship to clinical outcomes. We expect to initiate confirmatory clinical studies in the third quarter of 2026 in support of conditional approval pathways. If OST-HER2 receives approval under the FDA’s Accelerated Approval Program prior to September 30, 2029, we would become eligible to receive a Priority Review Voucher under the Rare Pediatric Disease Designation Program.

Upon success in gaining regulatory approval from the FDA with OST-HER2 in Osteosarcoma, we intend to evaluate OST-HER2’s potential use, both alone and in combination with HER2 targeting antibodies such as Herceptin®, in other solid tumors including breast, esophageal and lung cancers. OST-HER2 has potential uses in both the prevention of metastases in solid tumors, and therapeutically against HER2-expressing solid tumors treated with HER targeting antibodies.

We also own rights to an OST-Tunable Drug Conjugate (OST-tADC) platform, a next generation antibody-drug conjugate (ADC) silicone dioxide linker technology. “Tunable” is a term used in drug development that refers to the properties that can be influenced by chemical modifications, and “antibody-drug conjugate” or ADC is a term used to describe a drug made up of a monoclonal antibody attached to a cytotoxic payload, or a highly active and toxic pharmaceutical molecule, through chemical linkers. The ADC links an antibody that can home in on a targeted tumor to deploy the cytotoxic payload or toxic agent against the tumor. Furthering our founding mission, we intend to investigate clinical indications for OST-tADC in Osteosarcoma and other solid tumors.

Pipeline of Our Product Candidates

We have built a pipeline of product candidates targeting multiple indications for solid cancers. Our pipeline includes two drug technologies: (i) OST-HER2, an off-the-shelf immunotherapy, which is a type of cancer treatment that helps one’s immune system fight cancer, comprised of a genetically weakened and modified strain of Listeria monocytogenes, a species of bacteria that causes the infection listeriosis, that expresses HER2 peptides, and (ii) OST-tADC, a next generation tunable ADC with a plug-and-play platform that features tunable pH sensitive silicone linkers (SiLinkers™). The payloads may include antibodies, chemotherapeutics, cytotoxins and potentially mRNA treatments directly into and in the vicinity of solid tumors.

OST-HER2 (OST31-164). Our most advanced product candidate, OST-HER2, is a genetically engineered strain of Listeria monocytogenes, attenuated for reduced virulence, increased antibiotic susceptibility and the expression of three HER2 protein epitopes fused to immune-enhancing peptides on the membrane of the bacteria.

OST-HER2 has received an orphan drug designation in the United States. The FDA may designate a biologic product as an orphan product if it is intended to treat a rare disease or condition, which generally is defined as having a patient population of fewer than 200,000 individuals in the United States. Osteosarcoma has an incidence rate of approximately 1,000 individuals affected per year in the United States. Orphan product designation, subject to limited exceptions, can provide a period of market exclusivity for a product that is the first to receive marketing approval for the designated indication. Other potential indications may include breast, esophageal, lung and other solid tumors. In August 2021, OST-HER2 was awarded rare pediatric disease designation and previously received fast track designation by the FDA. Such designations by the FDA do not convey any advantages in, or shorten the duration of, the regulatory review or approval process.

OST-tADC. Our tunable drug conjugate (tADC) platform is currently in preclinical development. Each tADC contains four main components: ligand, payload cassette adaptor, linker and payload. In addition, tADCs contain units to optimize physicochemical properties. The ligands are selected to bind to receptors overexpressed on cancer cells. Upon binding, the tADC construct gets internalized into the cancer cell, where the payload is released, to cause cell death. The payload cassette adapters enable the stoichiometrical attachments of linkers and payloads. The SiLinkers represent a novel and pH-sensitive linker system. The SiLinker release profile can be tuned with proximal functional groups, resulting in payload release in the endosome, lysosome or the slightly acidic tumor microenvironment. The SiLinker system is compatible with a variety of payloads and not limited to the employment of cytotoxic drug delivery. The first set of internal programs focus on the use of SiLinker and conditionally active payloads (CAPs™) drug products. CAPs are cytotoxic drugs which on their own, due to their functional groups, cannot readily permeate cells at physiological pH; however, at the slightly acidic pH of the tumor-microenvironment, after some linker cleavage, these payloads readily permeate into cancer cells, resulting in an enhanced bystander effect. Our lead program targets folate receptor alpha, a protein expressed on the

SEC Form 10-K filed by OS Therapies Incorporated