Company Announcements

Recognized for Advancing (Z)-Endoxifen, a Precision-Engineered Endocrine Therapy with Potential Across Multiple Breast Cancer and Rare Disease Settings

SEATTLE , Dec. 17, 2025 /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, announces that it has 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 Duchenne Muscular Dystrophy (DMD).

"This award highlights our team's commitment to precision endocrine therapy and our integrated approach to developing (Z)-endoxifen for patients with high unmet medical needs," said Steven Quay, M.D., Ph.D., Atossa Therapeutics' President and Chief Executive Officer. "By combining biomarker-driven clinical studies, adaptive trial designs, and proactive regulatory engagement, we are advancing a therapy that has the potential to make a meaningful impact across multiple patient populations."

The Clinical Trials Arena Excellence Awards recognize companies and initiatives that demonstrate scientific rigor, innovation, and leadership in clinical research and drug development. Powered by GlobalData's business intelligence and independent analysis, the program evaluates more than one billion datasets annually to identify top-performing companies and technologies shaping the future of the life sciences industry.

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. Atossa's strategy emphasizes disciplined capital allocation, focusing resources on programs and data packages that can enable future regulatory submissions and potential commercialization. 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 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, 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 metastatic breast cancer indication, 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 regain and 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.

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SOURCE Atossa Therapeutics Inc