On December 4, 2025 Atossa Therapeutics, Inc. (Nasdaq: ATOS) ("Atossa" or the "Company"), a clinical-stage biopharmaceutical company focused on transforming breast cancer treatment and prevention, reported the completion of a Type C meeting with the U.S. Food and Drug Administration ("FDA") on November 17, 2025, to review regulatory strategy for advancing (Z)-endoxifen. During the meeting, the FDA provided the Company feedback on potential expedited regulatory pathways and development options across metastatic disease, neoadjuvant treatment, and breast cancer risk-reduction settings.

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The meeting focused on clinical development design, endpoint strategy, and pathways that could support a streamlined registrational approach. Atossa believes the FDA interaction meaningfully clarified potential routes to accelerate clinical development and regulatory review for (Z)-endoxifen, helping to position the Company to pursue a faster and more focused development strategy across multiple breast cancer indications.

"This meeting was a meaningful development milestone for our programs," said Steven Quay, M.D., Ph.D., Atossa’s President and Chief Executive Officer. "We used this discussion to incorporate FDA feedback into our development planning that could meaningfully shorten our regulatory timeline. We continue to aggressively execute the advancement of (Z)-endoxifen across the breast cancer continuum and toward potential registration pathways."

This includes multiple high-value 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.
In support of its metastatic breast cancer program, Atossa recently submitted an Investigational New Drug application ("IND") to the FDA and is awaiting feedback. The Company also anticipates additional IND submissions in 2026 to advance combination strategies and explore opportunities beyond monotherapy and breast cancer.

"Our clinical program is now structured around decisive value-creating milestones," said Janet Rea, MSPH, Senior Vice President of Research and Development. "We have completed multiple clinical trials involving nearly 800 participants, and are optimistic that this foundation, combined with anticipated upcoming data, and FDA input supports an active push towards multiple regulatory endpoints."

About (Z)-Endoxifen

(Z)-endoxifen is a highly potent Selective Estrogen Receptor Modulator/Degrader (SERM/D) with demonstrated ability to inhibit and potentially degrade estrogen receptors. It has shown activity even in tumors that have developed resistance to other endocrine therapies. Beyond its anti-estrogenic properties, (Z)-endoxifen also targets the oncogenic signaling pathway, protein kinase C beta 1 (PKCβ1), at clinically achievable blood and tumor levels. (Z)-endoxifen also seems to deliver comparable or superior bone-protective effects relative to tamoxifen.

Atossa is developing a proprietary enteric oral formulation of (Z)-endoxifen that bypasses stomach acid, which would otherwise partially convert the active (Z)-isomer to its inactive (E)-form. We believe this innovation allows for optimal bioavailability and therapeutic integrity. Clinical studies have shown Atossa’s (Z)-endoxifen to be well tolerated in both healthy women and those with breast cancer. In nearly 800 adults (healthy volunteers and breast cancer patients) receiving doses up to 360 mg/day, no maximum tolerated dose (MTD) has been identified, supporting continued dose-range exploration.

Atossa’s (Z)-endoxifen program is supported by a growing global intellectual property portfolio, including four recently issued U.S. patents and numerous pending applications worldwide.

(Press release, Atossa Therapeutics, DEC 4, 2025, View Source [SID1234661139])