Atossa Therapeutics Highlights 2025 Progress and 2026 Goals

Atossa Therapeutics, Inc. (Nasdaq: ATOS), a clinical-stage biopharmaceutical company based in Seattle, has released a shareholder letter detailing significant achievements in 2025 and outlining strategic goals for 2026. In the letter, Steven Quay, M.D., Ph.D., the company’s President and Chief Executive Officer, emphasized the advancements made with the company’s lead product candidate, (Z)-endoxifen, particularly in oncology.

Reflecting on 2025, Quay noted meaningful progress in advancing (Z)-endoxifen, a selective estrogen receptor modulator, towards critical regulatory and clinical milestones. The company refined its development strategy within oncology and identified additional opportunities for (Z)-endoxifen to address rare diseases with considerable unmet medical needs.

Regulatory Milestones and Clinical Advancements

A pivotal moment in Atossa’s strategy occurred in late 2025 with the completion of a Type C meeting with the U.S. Food and Drug Administration (FDA) on November 17. The meeting clarified regulatory pathways for (Z)-endoxifen in the treatment of breast cancer, including potential expedited development options for metastatic disease and risk-reduction settings.

Atossa is currently investigating (Z)-endoxifen within several “I-SPY 2” studies, focusing on its neoadjuvant role as both a monotherapy and in combination with other therapies. Preliminary data from the monotherapy arm showed encouraging results, where twenty women with newly diagnosed ER+/HER- breast cancer received daily doses of (Z)-endoxifen. The treatment was well tolerated and led to reductions in tumor activity markers and functional tumor volume.

Although the company submitted an Investigational New Drug (IND) application for a Phase 2 study in metastatic breast cancer and received approval to proceed, Atossa has chosen to pause further investment in this area. This decision allows the company to allocate resources towards higher-potential opportunities in oncology and other rare diseases.

Expanding Horizons: Non-Oncology Applications

In addition to its oncology applications, Atossa is exploring the therapeutic potential of (Z)-endoxifen for various rare diseases. Notably, the compound has garnered attention for its potential in treating Duchenne Muscular Dystrophy (DMD), a serious neuromuscular disorder. In late 2025, Atossa received two significant FDA designations for (Z)-endoxifen concerning DMD: the Rare Pediatric Disease Designation and the Orphan Drug Designation. These designations provide strategic benefits, including the potential for expedited reviews and market exclusivity.

Research is also underway regarding the implications of (Z)-endoxifen for women who are carriers of DMD, a population that may experience significant muscle-related symptoms. Atossa’s ongoing studies aim to develop hypotheses and clinical trial protocols to further explore these applications.

Additionally, Atossa is investigating McCune-Albright Syndrome (MAS), a rare genetic disorder that can lead to precocious puberty in young girls. The company believes (Z)-endoxifen could serve as an effective hormone blocker, reducing developmental complications associated with early onset puberty.

Strengthening Intellectual Property and Leadership

Throughout 2025, Atossa made strides in reinforcing its intellectual property portfolio, highlighted by the issuance of a U.S. patent for enteric oral formulations of (Z)-endoxifen. The company is actively defending its intellectual property amid ongoing litigation with Intas Pharmaceuticals Ltd., which seeks to challenge certain patents related to the manufacturing processes of (Z)-endoxifen.

Atossa also bolstered its leadership team by appointing key executives, including Janet R. Rea, MSPH, as Senior Vice President of Research and Development, and Mark Daniel, CPA, as Chief Financial Officer. These appointments are intended to enhance regulatory execution and prepare for future commercialization efforts.

Financial Resilience and 2026 Outlook

In terms of financial performance, Atossa entered 2026 with over $40 million in cash and cash equivalents, providing a solid foundation for ongoing operations. The company has also implemented a reverse stock split effective February 2, 2026, aimed at regaining compliance with Nasdaq listing requirements.

Looking ahead, Atossa plans to focus on expanding its intellectual property and business development capabilities while maintaining fiscal discipline. The company aims to drive measurable progress in its clinical programs and regulatory submissions throughout 2026.

Quay concluded the letter by reaffirming Atossa’s commitment to developing differentiated therapies that can meaningfully improve patient outcomes across a range of conditions, while also creating sustainable value for shareholders.

As Atossa Therapeutics embarks on 2026, it does so with a clear regulatory roadmap and an expanded clinical evidence base, poised to tackle both oncology and significant unmet needs in non-oncology areas.