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

SEATTLE, March 25, 2026 /PRNewswire/ — 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):

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