• New patent further strengthens global intellectual property estate supporting Atossa's lead program across the breast cancer spectrum and other hormone-driven conditions

SEATTLE, Dec. 9, 2025 /PRNewswire/ -- Atossa Therapeutics, Inc. (Nasdaq: ATOS) ("Atossa" or the "Company"), a clinical-stage biopharmaceutical company developing innovative therapies in areas of significant unmet need in breast cancer, today announced that the United States Patent and Trademark Office (USPTO) issued U.S. Patent No. 12,479,790 B2, titled, "Methods for Making and Using Endoxifen."

The newly issued patent includes 100 claims directed to enteric oral formulations of highly pure (Z)-endoxifen free base, as well as methods of using those compositions to treat a range of hormone-dependent breast disorders and other estrogen-related conditions. The patent also covers specific solid oral dosage forms and stable formulations providing therapeutically meaningful and sustained systemic exposure to (Z)-endoxifen.

"We believe this patent meaningfully extends and reinforces our already robust endoxifen patent estate," said Steven Quay, M.D., Ph.D., Atossa's President and Chief Executive Officer. "By covering both scalable manufacturing processes and key methods of use, this patent supports our long-term strategy to position (Z)-endoxifen as a differentiated therapy across the breast cancer spectrum, from risk-reduction and neoadjuvant treatment through adjuvant and metastatic disease, while also enabling opportunities in other hormone-driven conditions.

 "Together with previously issued U.S. patents covering storage-stable and sustained-release endoxifen formulations, and broader formulation patents granted earlier this year, this new patent further consolidates our leadership position in endoxifen therapeutics. A strong and durable intellectual property foundation is essential as we invest in late-stage clinical trials and potential future commercialization," concluded Dr. Quay.

Atossa is currently advancing its proprietary (Z)-endoxifen in multiple clinical settings, including:

• Metastatic breast cancer (MBC): A dose-ranging study is in preparation as part of the Company's strategy to support registrational development.
• Neoadjuvant ER+/HER2- breast cancer: Enrollment and data generation continue in the Phase 2 EVANGELINE trial.
• Breast cancer risk-reduction: Development includes a low-dose strategy targeting mammographic breast density and overall breast cancer risk.

The Company's growing patent portfolio, which now includes multiple issued U.S. patents and corresponding applications worldwide, is intended to provide long-term exclusivity for (Z)-endoxifen formulations, manufacturing processes, and key therapeutic uses in breast cancer treatment and risk reduction.

About U.S. Patent No. 12,479,790

U.S. Patent No. 12,479,790 B2, "Methods for Making and Using Endoxifen," is assigned to Atossa Therapeutics, Inc. The patent has 100 claims directed to enteric oral formulations of highly pure (Z)-endoxifen free base, as well as methods of using those compositions to treat a range of hormone-dependent breast disorders and other estrogen-related conditions. The patent also covers specific solid oral dosage forms and stable formulations providing therapeutically meaningful and sustained systemic exposure to (Z)-endoxifen.

About (Z)-Endoxifen

(Z)-endoxifen is one of the most potent selective estrogen receptor modulators (SERMs) for estrogen receptor inhibition and may also promote estrogen receptor degradation. It has demonstrated activity in settings where tumors have developed resistance to other hormonal therapies and has been shown to target PKCβ1, a known oncogenic protein, at clinically achievable concentrations. Atossa continues to optimize its proprietary oral formulation of (Z)-endoxifen, which is designed to minimize stomach exposure and maintain the active Z-isomer, and ensures consistent systemic exposure across a range of breast cancer prevention and treatment indications.

About Atossa Therapeutics

Atossa Therapeutics, Inc. (Nasdaq: ATOS) is a clinical-stage biopharmaceutical company developing innovative therapies in areas of significant unmet need in breast cancer. The Company's lead product candidate, (Z)-endoxifen, is being developed as a highly potent SERM for use across the breast cancer continuum of care. For more information, please visit www.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 timing thereof, the strength of the Company's patent portfolio, 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 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.