Atossa Therapeutics Presents Clinical Trial Update Highlighting (Z)-Endoxifen Research at the 2026 MDA Clinical & Scientific Conference

Study Highlights Findings that (Z)-endoxifen Restores Muscle Performance and Lowers Damage Biomarkers in mdx5Cv Dystrophic Mice

SEATTLE, March 12, 2026 /PRNewswire/ -- Atossa Therapeutics, Inc. (Nasdaq: ATOS) ("Atossa" or the "Company"), a clinical-stage biopharmaceutical company developing novel therapies in oncology and other rare disease indications with significant unmet need, presented an oral clinical trial update on (Z)-endoxifen at the MDA Clinical & Scientific Conference on March 11, 2026, in Orlando, FL.

Presentation Highlights

• The mdx5Cv Dystrophic mouse model, a trusted, reproducible standard for Duchenne muscular dystrophy (DMD) preclinical research, was used for this study
• (Z)-Endoxifen improved muscle strength and motor performance in both juvenile and adult dystrophic mice
• Treatment enhanced resistance to contraction-induced muscle injury
• Favorable changes were observed in body composition, including increased lean mass and reduced fat mass
• Key biochemical and histologic markers of muscle damage were reduced
• The therapy was well tolerated with no adverse findings observed during the study

Clinical Significance
DMD is a progressive and ultimately fatal neuromuscular disorder characterized by ongoing muscle degeneration, inflammation, and fibrosis. While current therapies have improved disease management, a significant unmet medical need for additional therapies remains.

The preclinical findings demonstrate that (Z)-endoxifen may address multiple aspects of DMD pathology, including muscle weakness, structural damage, and functional decline. These results support further clinical investigation of (Z)-endoxifen as a potential new therapeutic option.

"These findings demonstrate the potential of (Z)-endoxifen to meaningfully reduce muscle damage and potentially improve muscle performance in a nonclinical model of Duchenne muscular dystrophy," said Dr. Steven C. Quay, M.D., Ph.D., Chairman and Chief Executive Officer of Atossa Therapeutics. "We believe these data support continued clinical development of (Z)-endoxifen as a potential broad new therapeutic option for patients with DMD."

About Duchenne Muscular Dystrophy
Duchenne Muscular Dystrophy is a rare, progressive, neuromuscular disorder caused by one or more mutations in the dystrophin gene. Symptoms typically emerge in early childhood and include progressive muscle weakness, loss of ambulation, respiratory compromise, and cardiomyopathy. DMD is uniformly fatal, often in early adulthood, and despite recent therapeutic advances, there remains a substantial unmet medical need for safe, effective, and accessible treatments.

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 novel therapies 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. Atossa's strategy emphasizes disciplined capital allocation, focusing resources on programs and data packages that can enable future regulatory submissions and potential commercialization. For more information, visit www.atossatherapeutics.com and refer to Atossa's filings with the U.S. Securities and Exchange Commission (SEC).

Forward-Looking Statements
This press release contains certain "forward-looking statements" within the meaning of applicable securities laws, including but not limited to, our expectations regarding the Company's development and regulatory strategy and related milestones, the potential indications that the Company may pursue for (Z)-Endoxifen, the potential for (Z)-Endoxifen to receive regulatory approval and the timing thereof, expectations regarding the design, enrollment, data, timing, results and outcomes of the Company's clinical studies, 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 for oncology indications, 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 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.

SOURCE Atossa Therapeutics Inc