R&D spending jumps as Atossa (NASDAQ: ATOS) advances (Z)-endoxifen programs

Rhea-AI Filing Summary

Atossa Therapeutics reported a larger net loss of $34.8M for the year ended December 31, 2025, compared with $25.5M a year earlier, as it increased investment in its lead drug candidate, (Z)-endoxifen.

Total operating expenses rose to $37.1M from $27.6M. Research and development spending climbed 50% to $21.2M, driven mainly by an extra $6.1M on clinical and non-clinical trials and higher regulatory consulting tied to (Z)-endoxifen. General and administrative costs increased 18% to $16.0M, reflecting higher legal expenses related to litigation and patent defense and modestly higher compensation.

The company ended 2025 with cash and cash equivalents of $41.3M, down from $71.1M as it funded operations, while interest income fell to $2.4M from $4.1M due to lower average invested balances. During the year, Atossa secured FDA Rare Pediatric Disease and Orphan Drug designations for (Z)-endoxifen in Duchenne Muscular Dystrophy and strengthened its clinical leadership team to support both breast cancer and rare disease programs.

Insights

Biotech equity analyst

Atossa is increasing R&D spending and narrowing its focus on (Z)-endoxifen while drawing down cash.

Atossa Therapeutics is still pre-revenue and reported a higher net loss of $34.8M in 2025, mainly because total operating expenses rose to $37.1M. The largest driver was a 50% increase in research and development to $21.2M, focused on (Z)-endoxifen trials and regulatory work.

General and administrative costs increased 18% to $16.0M, with legal expenses rising by about $1.8M due to ongoing litigation and patent defense, partly offset by lower insurance and accounting fees. Interest income declined to $2.4M as average cash balances fell.

Cash and cash equivalents declined to $41.3M from $71.1M, while liabilities remained modest at $8.2M. Atossa highlighted FDA Rare Pediatric Disease and Orphan Drug designations for (Z)-endoxifen in Duchenne Muscular Dystrophy and added senior medical leaders, which together underscore a strategy centered on advancing this lead asset in oncology and rare diseases.

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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): March 25, 2026

Atossa Therapeutics, Inc.

(Exact name of Registrant as Specified in Its Charter)

Delaware			001-35610	26-4753208
(State or Other Jurisdiction of Incorporation)			(Commission File Number)	(IRS Employer Identification No.)
1448 NW Market Street, Suite 500
Seattle, Washington				98107
(Address of Principal Executive Offices)				(Zip Code)

Registrant’s Telephone Number, Including Area Code: (206) 588-0256

N/A

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐	Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)
☐	Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)
☐	Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))
☐	Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

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, $0.18 par value		ATOS		The Nasdaq Capital Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

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. ☐

Item 2.02. Results of Operations and Financial Condition.

On March 25, 2026, Atossa Therapeutics, Inc. (the “Company”) issued a press release announcing the fourth quarter and year ended December 31, 2025 financial results and providing a Company update. A copy of the press release is attached as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated herein by reference.

The information in Items 2.02 and 9.01 of this report, including Exhibit 99.1 attached hereto, shall not be deemed to be “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that Section or Sections 11 and 12(a)(2) of the Securities Act of 1933, as amended. The information contained herein and in the accompanying exhibit shall not be incorporated by reference into any filing with the U.S. Securities and Exchange Commission made by the Company, whether made before or after the date hereof, regardless of any general incorporation language in such filing.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits

Exhibit No.		Description
99.1		Press Release dated March 25, 2026
104		Cover page Interactive Data File (embedded within the Inline XBRL document)

* * *

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

			Atossa Therapeutics, Inc.
Date:	March 25, 2026	By:	/s/ Mark J. Daniel
			Mark J. Daniel Chief Financial Officer (Principal Financial and Accounting Officer)

Exhibit 99.1

Atossa Therapeutics Reports Fourth Quarter and Year-End 2025 Financial Results and Provides a Corporate Update

SEATTLE, March 25, 2026 — Atossa Therapeutics, Inc. (Nasdaq: ATOS) (Atossa or the Company), a clinical-stage biopharmaceutical company developing novel therapies in oncology and other areas of high unmet clinical need, today announces its financial results for the fourth quarter and year ended December 31, 2025 and provides an update on recent corporate developments.

“While we have consistently made meaningful and measurable progress across our (Z)-endoxifen development strategy in oncology over the last 12 months, we continue to explore the best opportunities to leverage the technology where it may help to address serious health conditions and unmet medical needs. As we continue to keep a careful eye on opportunities in the breast cancer space, we are also diligently working to advance (Z)-endoxifen in certain rare disease indications, such as Duchenne Muscular Dystrophy (DMD) and McCune-Albright Syndrome (MAS),” stated Dr. Steven Quay, M.D., Ph.D., Atossa Therapeutics’ President and Chief Executive Officer. “To date, we have published work that identifies the opportunity for (Z)-endoxifen, while achieving both FDA Rare Pediatric Disease and Orphan Drug designations. We believe these FDA designations are important for future development as they both help to speed the FDA review process as well as provide potential financial benefits in the future.”

“In the meantime, we are consciously aligning our resources with the demands of potential commercialization, even as we have added new professionals to our team to help drive both our rare disease and breast cancer programs forward. With a strong balance sheet and a strategically focused team, we believe we are well-positioned to execute and advance our clinical programs toward key value-creating milestones,” concluded Dr. Quay.

Clinical & Regulatory Progress & Announcements

•Atossa Highlighted Emerging Opportunity for (Z)-Endoxifen in Duchenne Muscular Dystrophy, Including Symptomatic Female Carriers, Following Peer-Reviewed Publication and Scientific Presentation - The published article, “A Hypothesized Therapeutic Role of (Z)-Endoxifen in Duchenne Muscular Dystrophy (DMD),” surveys the DMD treatment landscape and details how (Z)-endoxifen’s pharmacology could address multiple downstream drivers of disease, including inflammation, fibrosis, calcium dysregulation, mitochondrial dysfunction, and lipid abnormalities. The paper emphasizes (Z)-endoxifen’s direct estrogen-receptor (ER) modulation, allosteric inhibition of PKC (notably PKC-β1), and effects along AKT/mTOR and NF-κB axes, mechanisms that together may help slow disease progression when used as an adjunct to standard care. Notably, the authors underscore (Z)-endoxifen’s potential to deliver more consistent therapeutic exposures than tamoxifen by bypassing CYP2D6 metabolic variability, an important limitation of the pro-drug approach. As illustrated in the mechanistic diagram, page 7 of the publication, the paper maps (Z)-endoxifen’s ER-dependent and ER-independent signaling effects relevant to dystrophic muscle.

•Atossa Therapeutics Received FDA Rare Pediatric Disease Designation for (Z)-Endoxifen for Duchenne Muscular Dystrophy - In December 2025, Atossa announced that the U.S. Food and Drug Administration (“FDA”) granted Rare Pediatric Disease (“RPD”) designation to (Z)-endoxifen for the treatment of DMD. RPD designation is granted to drug candidates intended to treat serious or life-threatening diseases that primarily affect individuals from birth to 18 years of age. Upon approval of a qualifying marketing application, drugs with RPD designation may be eligible for a Priority Review Voucher (“PRV”), which can be used to obtain priority review for a future application or may be sold or transferred to another sponsor. In the last 18–24 months, disclosed PRV sales have ranged from $100–$200 million.

•Atossa Therapeutics Won the 2025 Clinical Trials Arena Research and Development Excellence Award in Precision Endocrine Therapy Category - In December 2025, Atossa announced that it had been selected as a winner of the 2025 Clinical Trials Arena Excellence Awards. The Company was honored with the Research and Development Award in the Precision Endocrine Therapy category. Atossa earned this recognition for its innovative work advancing (Z)-endoxifen, its lead precision-engineered endocrine therapy. (Z)-endoxifen is a potent selective estrogen receptor modulator/degrader (SERM/D) with additional PKCβ1 inhibition, designed to provide consistent systemic exposure independent of CYP2D6 metabolism. The

therapy is being evaluated across metastatic, neoadjuvant, adjuvant, and breast cancer risk-reduction settings, with an emerging application in DMD.

•Atossa Therapeutics Received FDA Orphan Drug Designation for (Z)-Endoxifen for the Treatment of Duchenne Muscular Dystrophy - In January 2026, Atossa announced that the U.S. Food and Drug Administration (“FDA”) Office of Orphan Products Development (“OOPD”) granted Orphan Drug Designation to (Z)-endoxifen for the treatment of DMD. Orphan Drug Designation is granted by FDA to therapies intended to treat rare diseases or conditions. The designation is designed to encourage drug development by offering certain potential incentives, such as regulatory support and, if the product ultimately receives marketing approval for the designated indication, eligibility for a period of market exclusivity.

Atossa Announces Additions to Management Team

•Atossa Therapeutics Strengthened Clinical Leadership Team with the Addition of Two Experienced Biopharma Executives - Atossa announced the engagement of Kathy Puyana Theall, M.D., as Medical Director - Breast Oncology, and Adebola Giwa, M.D., as Medical Director - Rare Diseases. We believe the addition of these two highly experienced physicians and clinical leaders meaningfully strengthens Atossa’s ability to execute on its (Z)-endoxifen development strategy across both breast cancer and rare disease programs, including DMD and MAS, as the Company advances toward key clinical and regulatory milestones.

Comparison of Years-Ended December 31, 2025 and 2024

Operating Expenses. Total operating expenses were $37.1 million for the year ended December 31, 2025, which was an increase of $9.5 million, from the year ended December 31, 2024 of $27.6 million. Factors contributing to the increased operating expenses in the year ended December 31, 2025 are explained below.

Research & Development Expenses. The following table provides a breakdown of major categories within R&D expenses for the years ended December 31, 2025 and 2024, together with the dollar change in those categories (dollars in thousands):



	For the Year Ended December 31,
	2025	2024	Increase	Increase (%)
Research and Development Expense
Clinical and non-clinical trials	$16,204	$10,107	$6,097	60%
Compensation	3,206	2,928	278	9%
Professional fees and other	1,775	1,082	693	64%
Research and Development Expense Total	$21,185	$14,117	$7,068	50%

As (Z)-endoxifen is our only product candidate for which we currently incur R&D expenses, we have not further disaggregated R&D expenses by product candidate:

•Clinical and pre-clinical trial expense increased $6.1 million for the year ended December 31, 2025 compared to the prior year due to an increase in spending for the (Z)-endoxifen trials, including an increase in drug development costs.

•The increase in R&D compensation expense of $0.3 million for the year ended December 31, 2025 compared to the prior year was due primarily to an increase in cash compensation expense of $0.4 million resulting from an increase in headcount. This increase was partially offset by a non-cash stock-based compensation expense decrease of $0.1 million compared to the prior year due to the weighted average fair value of stock options amortizing in 2025 being lower than 2024.

•The increase in R&D professional fees and other of $0.7 million for the year ended December 31, 2025 compared to the prior year was primarily attributable to higher regulatory consulting fees in 2025 related to our (Z)-endoxifen program.

General and Administrative (G&A) Expenses. The following table provides a breakdown of major categories within G&A expenses for the years ended December 31, 2025 and 2024, together with the dollar change in those categories (dollars in thousands):



For the Year Ended December 31,

	2025	2024	Increase (Decrease)	Increase (%) (Decrease)
General and Administrative Expense
Compensation	$6,062	$5,458	$604	11%
Professional fees and other	9,191	7,164	2,027	28%
Insurance	703	882	(179)	(20)%
General and Administrative Expense Total	$15,956	$13,504	$2,452	18%

•The increase in G&A compensation expense of $0.6 million for the year ended December 31, 2025 compared to the prior year was due to an increase in both cash compensation expense of $0.2 million and non-cash stock-based compensation expense of $0.4 million. The increase in cash compensation expense compared to the prior year was primarily driven by salary, bonus and severance costs for a former executive of $0.4 million, partially offset by a decrease in cash bonus related to terminations and reductions in expected bonus payouts in 2025. The non-cash stock-based compensation expense increase was driven by an increase in the fair value of grants to members of our Board of Directors (the Board) which amortize over one year.

•G&A professional fees and other expenses increased by $2.0 million for the year ended December 31, 2025 compared to the prior year due primarily to an increase in legal fees of $1.8 million for the year ended December 31, 2025 driven by the costs for our ongoing litigation and patent defense which increased by $1.6 million compared to the prior year. Investor relations expense increased by $0.3 million for the year ended December 31, 2025 compared to the prior year due to changes in investor outreach and broader investor relations strategy. Partially offsetting the increases, our accounting fees decreased by $0.3 million for the year ended December 31, 2025 compared to the prior year due to the inclusion of higher auditor fees associated with our 2024 Registration Statement on Form S-3 and our at the market offering facility.

•The decrease in G&A insurance expense of $0.2 million for the year ended December 31, 2025 compared to the prior year was due primarily to lower negotiated insurance premiums associated with our Director's and Officer's insurance and other key insurance policies in 2025.

Interest Income. Interest income of $2.4 million for the year ended December 31, 2025 represented a decrease of $1.7 million compared to the prior year, and was due primarily to a decrease in the average funds invested in our money market account.

Impairment Charge on Investment in Equity Securities. For the year ended December 31, 2024, we wrote down our Investment in equity securities by $1.7 million due to impairment of our investment in Dynamic Cell Therapies, Inc.



About (Z)-Endoxifen

(Z)-Endoxifen is a potent Selective Estrogen Receptor Modulator/Degrader (SERM/D) with demonstrated activity across multiple mechanisms of interest. Atossa is evaluating its potential applications in oncology and rare diseases. The Company’s proprietary oral formulation has shown a favorable safety profile and pharmacology distinct from tamoxifen, including ER-targeted effects and PKC inhibition. Atossa’s (Z)-endoxifen is not approved for any indication.

Atossa’s (Z)-endoxifen program is supported by a growing global intellectual property portfolio, including multiple recently issued U.S. patents and numerous pending applications worldwide.

About Atossa Therapeutics

Atossa Therapeutics, Inc. (Nasdaq: ATOS) is a clinical-stage biopharmaceutical company developing innovative medicines in oncology and other areas of significant unmet need. The Company’s lead product candidate, (Z)-endoxifen, is currently in development across several clinical settings. More information is available at https://atossatherapeutics.com.

Forward Looking Statements

This press release contains certain “forward-looking statements” within the meaning of applicable securities laws, including but not limited to, our 2026 outlook and our expectations regarding the Company’s development and regulatory strategy and related milestones, including potential Investigational New Drug submissions, the potential indications that the Company may pursue for (Z)-endoxifen, the potential for (Z)-endoxifen to receive regulatory approval and the timing thereof, the Company's progress across its pipeline and potential commercialization, the strength of the Company's patent portfolio, the Company’s potential eligibility for the Rare Pediatric

Disease Priority Review Voucher (PRV) program and the value of a PRV, and the potential market and growth opportunities for the Company. Words such as “expect,” “potential,” “continue,” “may,” “will,” “should,” “could,” “would,” “seek,” “intend,” “plan,” “estimate,” “anticipate,” “believe,” “design,” “predict,” “future,” or other similar expressions or statements regarding intent, belief or current expectations, are forward-looking statements.

Forward-looking statements in this press release are subject to risks and uncertainties that may cause actual results, outcomes, or the timing of actual results or outcomes to differ materially from those projected or anticipated, including, without limitation, risks and uncertainties associated with: our ability to successfully execute our strategy to shorten our clinical development timelines and pursue a DMD indication or other indications for our lead program, (Z)-endoxifen; expected timing, completion and results of our preclinical studies, clinical trials and research and development programs; the unpredictable relationship between preclinical study results and clinical study results; the timing or likelihood of regulatory filings and approvals; the outcome or timing of necessary regulatory approvals; our ability to receive orphan-drug exclusivity for (Z)-endoxifen for DMD; our ability to maintain compliance with Nasdaq listing requirements; our ability to establish and maintain intellectual property rights covering our products; the impact of general macroeconomic conditions on our business; our ability to raise capital; and other risks and uncertainties detailed from time to time in Atossa’s filings with the SEC, including, without limitation, its Annual Reports on Form 10-K and Quarterly Reports on Form 10-Q.

Forward-looking statements are presented as of the date of this press release. Except as required by law, we do not intend to update any forward-looking statements.

Investor & Media Contact

Investors: CORE IR — ir@atossatherapeutics.com • (212) 655-0924

Media: CORE IR — pr@atossatherapeutics.com • (212) 655-0924

ATOSSA THERAPEUTICS, INC.

CONSOLIDATED BALANCE SHEETS

(amounts in thousands, except share and per share data)

	December 31, 2025		December 31, 2024
Assets
Current assets
Cash and cash equivalents	$	41,299	$	71,084
Restricted cash		110		110
Prepaid materials		3,081		2,098
Prepaid expenses and other current assets		1,128		1,165
Total current assets		45,618		74,457
Other assets		1,990		1,987
Total assets	$	47,608	$	76,444
Liabilities and stockholders' equity
Current liabilities
Accounts payable	$	4,293	$	679
Accrued expenses		1,307		919
Payroll liabilities		1,558		1,862
Other current liabilities		1,097		1,507
Total current liabilities		8,225		4,967
Total liabilities		8,225		4,967
Commitments and contingencies
Stockholders' equity
Convertible preferred stock - $0.001 par value; 10,000,000 shares authorized; 577 and 582 shares issued and outstanding as of December 31, 2025 and December 31, 2024, respectively		—		—
Common stock - $0.18 par value; 350,000,000 shares authorized; 8,611,361     and 8,611,266 shares issued and outstanding as of December 31, 2025 and     December 31, 2024, respectively		1,550		1,550
Additional paid-in capital		285,840		283,194
Treasury stock, at cost; 88,003 shares of common stock at December 31, 2025 and December 31, 2024		(1,475)		(1,475)
Accumulated deficit		(246,562)		(211,792)
Total stockholders' equity		39,353		71,477
Total liabilities and stockholders' equity	$	47,608	$	76,444

ATOSSA THERAPEUTICS, INC.

CONSOLIDATED STATEMENTS OF OPERATIONS

(amounts in thousands, except share and per share data)

	For the Year Ended December 31,
	2025	2024
Operating expenses
Research and development	$ 21,185	$ 14,117
General and administrative	15,956	13,504
Total operating expenses	37,141	27,621
Operating loss	(37,141)	(27,621)
Impairment charge on investment in equity securities	—	(1,710)
Interest income	2,377	4,050
Other expense, net	(6)	(223)
Loss before income taxes	(34,770)	(25,504)
Income tax benefit	—	—
Net loss	$ (34,770)	$ (25,504)
Net loss per share of common stock - basic and diluted	$ (4.04)	$ (3.04)
Weighted average shares outstanding used to compute    net loss per share - basic and diluted	8,611,321	8,6390,618

FAQ

How did Atossa Therapeutics (ATOS) perform financially in 2025?

Atossa reported a net loss of $34.8 million for 2025, compared with $25.5 million in 2024. The wider loss reflects higher operating expenses as the company increased research, clinical activity, and legal spending while remaining in a pre-revenue, clinical-stage development phase.

How much did Atossa Therapeutics spend on R&D in 2025?

Atossa’s research and development expenses were $21.2 million in 2025, up from $14.1 million in 2024. The 50% increase was mainly due to an additional $6.1 million on (Z)-endoxifen clinical and non-clinical trials and higher regulatory consulting fees.

What was Atossa Therapeutics’ cash position at year-end 2025?

At year-end 2025, Atossa held $41.3 million in cash and cash equivalents, compared with $71.1 million at year-end 2024. The decline reflects funding of higher operating expenses as the company advances (Z)-endoxifen, while maintaining relatively low total liabilities of $8.2 million.

What regulatory designations did (Z)-endoxifen receive for Duchenne Muscular Dystrophy?

(Z)-endoxifen received FDA Rare Pediatric Disease designation in December 2025 and Orphan Drug designation in January 2026 for Duchenne Muscular Dystrophy. These designations may provide regulatory support and potential incentives, including possible eligibility for a Priority Review Voucher upon future approval.

How did Atossa Therapeutics’ general and administrative expenses change in 2025?

General and administrative expenses rose to $16.0 million in 2025 from $13.5 million in 2024. The increase was driven mainly by higher legal fees of about $1.8 million for litigation and patent defense, along with higher compensation, partly offset by lower insurance and accounting costs.

What strategic focus did Atossa highlight for (Z)-endoxifen?

Atossa emphasized (Z)-endoxifen as its lead product candidate, advancing it in breast cancer and rare disease indications such as DMD and MAS. The company noted a favorable safety profile, distinct pharmacology from tamoxifen, and a growing intellectual property portfolio supporting ongoing and planned clinical development.

Filing Exhibits & Attachments

2 documents

Press Releases

• EX-99.1 EX-99.1 155.9 KB

Other Documents

• EX-101 XBRL TAXONOMY EXTENSION SCHEMA WITH EMBEDDED LINKBASES DOCUMENT 26.3 KB