Atossa Therapeutics Highlights Progress in RECAST™ DCIS Platform Trial at Early Detection Research Conference; Laura Esserman, MD, MBA, to Discuss Active-Surveillance Strategy and Novel Endocrine Agents

Investor-focused update underscores enrollment momentum, biomarker strategy, and near-term data readouts designed to de-risk development of (Z)-Endoxifen and other endocrine therapies for DCIS

SEATTLE, Oct. 21, 2025 /PRNewswire/ -- Atossa Therapeutics, Inc. (Nasdaq: ATOS) ("Atossa" or the "Company"), a clinical-stage biopharmaceutical company developing innovative medicines in oncology, today announced that Laura J. Esserman, MD, MBA, Professor of Surgery and Radiology at the University of California, San Francisco and Principal Investigator of RECAST™, will speak at the Early Detection Research Conference in Portland, OR, about the Company's collaborative work in the RECAST platform trial for ductal carcinoma in situ (DCIS), a biologically heterogeneous, non-invasive breast condition that can progress to invasive breast cancer in a subset of patients.

RECAST is a multi-arm, Phase 2, randomized, neoadjuvant platform trial designed to identify which patients with hormone receptor–positive DCIS are best suited for active surveillance and to determine whether novel endocrine therapies can expand the population that can safely avoid surgery. The trial includes arms evaluating standard therapy (tamoxifen or aromatase inhibitor) as well as novel agents: (Z)-Endoxifen, elacestrant, and Hav-088. Efficacy is assessed with mammography and breast MRI, alongside biomarker discovery and quality-of-life endpoints. Enrollment began in January 2024; 50 patients have been enrolled toward a target of 400 across 17 activated clinical sites, with additional sites planned.

Why this matters for investors

• Large, under-served market: DCIS is commonly treated like invasive cancer (surgery ± radiation ± endocrine therapy). Demonstrating that a biomarker-guided, non-surgical approach is safe and effective could reshape standard of care and expand use of oral endocrine agents in early-stage disease management.
• Efficient signal-finding: The platform design enables parallel testing of multiple agents, including Atossa's (Z)-Endoxifen, with common imaging and biomarker endpoints to generate comparative signals that can inform registration strategies.
• Multiple potential catalysts: Early imaging response, biomarker correlation, and active-surveillance suitability rates by arm create interim readout opportunities that can de-risk later-stage programs and guide payer-relevant health-economic modeling.
• Strategic collaborations: RECAST is sponsored by Quantum Leap Healthcare Collaborative with research support from NIH and industry partners. This shared-infrastructure model can accelerate enrollment, broaden site access, and optimize capital efficiency.

"RECAST is purpose-built to answer the question that payers, physicians, and patients care most about: who truly needs surgery and who does not," said Steven Quay, MD, PhD, Chairman and CEO of Atossa Therapeutics. "For Atossa, the trial offers a capital-efficient path to demonstrate the potential of (Z)-Endoxifen in a large early-disease setting, generate decision-grade biomarkers, and position us for value-creating milestones over the coming quarters."

RECAST Trial Objectives

1. Increase the fraction of DCIS patients suitable for long-term active surveillance using novel endocrine therapy.
2. Correlate risk of progression to invasive ductal carcinoma with risk categorization after six months of therapy.
3. Identify biomarkers that predict response and elucidate mechanisms of imaging response and resistance.
4. Assess quality of life compared with standard endocrine therapy.

Current Trial Status

• Phase: 2 (platform)
• Population: HR-positive DCIS (any grade)
• Arms: Tamoxifen/AI (control), (Z)-Endoxifen, elacestrant, Hav-088
• Assessments: Mammogram, MRI, biomarker panels, QoL
• Enrollment: 50/400; 17 active U.S. sites; additional site activations planned.

About Atossa Therapeutics

Atossa Therapeutics, Inc. (Nasdaq: ATOS) is a clinical-stage biopharmaceutical company developing novel therapies in oncology, including (Z)-Endoxifen, to improve outcomes for patients across the breast cancer continuum of care. Information about Atossa can be found at the website: https://atossatherapeutics.com/. Information about the conference can be found here: https://www.earlydetectionresearch.com/

Forward-Looking Statements

This press release contains forward-looking statements, including statements regarding the design, conduct, timing, and potential impact of the RECAST trial; the development, safety, and efficacy of (Z)-Endoxifen and other endocrine therapies; potential changes to standards of care; anticipated milestones, data readouts, regulatory interactions, and market opportunities; and the benefits of collaborative platform trials. These statements are subject to risks and uncertainties that could cause actual results to differ materially, including those described in Atossa's filings with the SEC. Atossa undertakes no obligation to update forward-looking statements except as required by law.

SOURCE Atossa Therapeutics Inc