Changes are expected to reduce future study costs, accelerate objective readouts, and extend operating runway under current plans

SEATTLE , Oct. 6, 2025 /PRNewswire/ -- Atossa Therapeutics, Inc. (Nasdaq: ATOS; "Atossa" or the "Company), a clinical-stage biopharmaceutical company developing new approaches in breast cancer treatment and prevention, announces an amendment to its Phase 2 EVANGELINE study of (Z)-endoxifen in premenopausal women with newly diagnosed early-stage ER+/HER2- breast cancer. The amended, non-registrational design is expected to accelerate objective readouts while reducing projected future study costs, consistent with Atossa's focus on extending operating runway and deploying capital where it is most impactful. In 2026, Atossa is concentrating its resources on near-term, NDA-enabling activities for investigational (Z)-endoxifen.

"This amendment is about efficiency, focus, and financial discipline," said Steven Quay, M.D., Ph.D., Atossa's Chairman and Chief Executive Officer. "By streamlining EVANGELINE, we are rationalizing study spending and concentrating our strong balance sheet on the NDA-enabling package we plan to advance in 2026, without changing our safety oversight or commitment to rigorous data."

Capital Allocation Highlights

• Prioritizing runway and catalysts: The amended design is expected to reduce future EVANGELINE study costs and further focus on NDA-enabling work under Atossa's 2025-2026 operating plan
• Faster, objective decision points: Cohort A patients with an initial Ki-67 of > 10% employ a pre-specified two-stage futility rule using short-interval, objective endpoints (e.g., Week-4 Ki-67 ≤10%) to enable earlier go/no-go decisions. Cohort B will be for patients with initial Ki-67 of < 10%
• Safety unchanged: There is no change to patient-safety data collection or Data Safety Monitoring Committee (DSMC) oversight with this amendment
• Operational focus: A single-arm, open-label structure concentrates efforts on one regimen and the data elements most relevant to a future NDA

EVANGELINE Design Snapshot (As Amended)

• Study type: Single-arm, open-label, non-registrational Phase 2 in premenopausal women with ER+/HER2– breast cancer in the pre-surgical setting
• Cohort A (signal-seeking): Two-stage futility design assessing the Week-4 Ki-67 ≤10% rate to allow early stop if not promising
• Cohort B (estimation): Week-24 objective response (RECIST 1.1, central review)
• Rationale: Focus on objective, short-interval endpoints to inform development decisions efficiently while preserving patient safeguards
• Study size change: The original EVANGELINE study design included 214 patients. This amendment reduces the patient total to 40-65 patients

Clinical context

EVANGELINE run-in data previously presented at the 2024 San Antonio Breast Cancer Symposium showed a Week-4 Ki-67 ≤10% rate of 86% across evaluated (Z)-endoxifen dose levels with/without Ovarian Function Suppression (OFS). In 2021, Atossa reported an 86% response rate of Ki-67 < 10% for women on low dose (4 mg/day) endoxifen in the same pre-surgery neoadjuvant setting. Published comparators in similar settings report a 41% response rate with tamoxifen and a 78% response rate with an aromatase inhibitor and OFS (Nitz UA, et al., J Clin Oncol. 2022 Aug 10;40(23):2557-2567). However, no efficacy conclusions can be drawn from the ongoing study at this point. There is no change to patient safety data collection or Data Safety Monitoring Committee oversight by this amendment.

ABOUT EVANGELINE

EVANGELINE is a single-arm, open-label, non-registrational Phase 2 study evaluating investigational (Z)-endoxifen in premenopausal women with ER+/HER2– breast cancer in the pre-surgical setting. The trial uses short-interval, objective endpoints with a pre-specified two-stage futility rule to enable faster, data-driven decisions.

Participating U.S. centers include: Mayo Clinic Rochester; Mayo Clinic Arizona; Mayo Clinic Florida; Washington University School of Medicine; St. Elizabeth Healthcare; Bon Secours Cancer Institute; Vanderbilt-Ingram Cancer Center; Henry Ford Cancer Institute; Fred Hutch; Dana-Farber Cancer Institute; Baylor University; University of Arizona; Northwestern University; Avera Cancer Institute; and California Research Institute. For current site activation status and updates, see ClinicalTrials.gov (NCT05607004).

ABOUT (Z)-ENDOXIFEN

(Z)-endoxifen is an investigational, active metabolite of tamoxifen being developed by Atossa for hormone receptor–positive breast-cancer settings. Its safety and efficacy have not been established.

ABOUT ATOSSA THERAPEUTICS

Atossa Therapeutics, Inc. (Nasdaq: ATOS) is a clinical-stage biopharmaceutical company developing innovative therapies for significant unmet needs in breast cancer. 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 the Company's website at 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 forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, including statements regarding the anticipated impact of the EVANGELINE amendment; expected reductions in future study costs; expected timelines, operating runway, and capital allocation; and plans for NDA-enabling activities in 2026. Forward-looking statements are based on current expectations and are subject to risks and uncertainties that could cause actual results to differ materially. These risks include, without limitation, clinical, regulatory, operational, financial, and market risks; the possibility that study timelines or costs differ from current expectations; that clinical results may not support further development or regulatory submissions; and other risks described in Atossa's most recent periodic reports filed with the SEC, including the "Risk Factors" sections therein. Atossa undertakes no obligation to update forward-looking statements except as required by law.

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SOURCE Atossa Therapeutics Inc