Atossa Therapeutics Announces ASCO 2026 Abstracts Highlighting (Z)-Endoxifen Activity Across ESR1 Mutations and Ongoing EVANGELINE Phase 2 Trial

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Preclinical Data Abstract Demonstrates Robust Estrogen Receptor (ER) Inhibition in ESR1-Mutant Breast Cancer Models at Clinically Relevant Concentrations Trial-in-Progress Abstract Details Ongoing Phase 2 EVANGELINE Study of (Z)-Endoxifen Plus Goserelin as Neoadjuvant Therapy in Premenopausal Women With ER+/HER2- Breast Cancer SEATTLE, May 27, 2026 /PRNewswire/ -- Atossa Therapeutics, Inc. (Nasdaq: ATOS) ("Atossa" or the "Company"), a clinical-stage biopharmaceutical company developing novel therapies in oncology and other areas of significant unmet medical need, today announced that two abstracts featuring (Z)-endoxifen have been accepted for presentation at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting, being held May 29 to June 2, 2026 in Chicago, IL. "Both abstracts highlight the scientific rationale and ongoing clinical development of (Z)-endoxifen in ER-positive breast cancer," said Dr. Steven C. Quay, M.D., Ph.D., President and Chief Executive Officer of Atossa Therapeutics. "Our preclinical data demonstrate that (Z)-endoxifen achieved robust estrogen receptor inhibition across clinically relevant ESR1 mutations associated with endocrine resistance, while the EVANGELINE trial is evaluating its potential in combination with ovarian function suppression in premenopausal women in the neoadjuvant setting. Together, these abstracts underscore our belief that (Z)-endoxifen has the potential to address important unmet needs across multiple treatment settings in ER-positive breast cancer." Presentation details are as follows: Session Type: Online PublicationAbstract Title: Effect of (Z)-endoxifen Demonstrates Robust Estrogen Receptor Signaling Inhibition Across Clinically Relevant ESR1 Mutations Summary: The abstract highlights new preclinical data demonstrating that (Z)-endoxifen delivers robust ER inhibition across clinically relevant estrogen receptor alpha gene (ESR1) mutations. ESR1 mutations are a major mechanism of acquired endocrine resistance in ER-positive breast cancer and remain associated with limited treatment options despite the emergence of next-generation endocrine therapies. These data therefore support the ongoing clinical development of (Z)-endoxifen, as well as its potential as a promising treatment option for breast cancer patients with limited therapeutic alternatives. Ke...

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