Endoxifen

Studies highlight findings regarding the potential use of (Z)-endoxifen to advance breast cancer treatment and risk reduction SEATTLE, Dec. 15, 2025 /PRNewswire/ -- Atossa Therapeutics, Inc. (Nasdaq: ATOS) ("Atossa" or the "Company"), a clinical-stage biopharmaceutical company developing innovative medicines in oncology and other areas of high unmet need, presented four clinical trial updates on (Z)-endoxifen at the San Antonio Breast Cancer Symposium (SABCS), held December 9-12, 2025, in San Antonio, TX. "Clinical trial updates and data presented at SABCS 2025 reinforce our focus on the therapeutic value of (Z)-endoxifen across the breast care continuum," said Steven Quay, M.D., Ph.D., Atossa Therapeutics' President and Chief Executive Officer. "With support from our growing body of clinical evidence, we continue to advance our high value clinical programs. Following our more streamlined pathway for our Phase 2 EVANGELINE study, we expect continued enrollment and data generation for neoadjuvant ER+/HER2- breast cancer. Finally, we are committed to advancing a low-dose treatment strategy designed to reduce mammographic breast density. High mammographic breast density has been associated with a higher risk of developing future breast cancer." Presentation Highlights: Initial results from RECAST DCIS: Multicenter platform trial testing active surveillance and novel endocrine therapy agents for DCIS management Clinical significance Early RECAST findings suggest that short-term endocrine therapy combined with MRI response assessment may identify patients with low-risk DCIS who can avoid surgery and pursue active surveillance, offering a potential pathway to reduce overtreatment while personalizing care Key takeaways RECAST is testing whether short-term endocrine therapy plus MRI response can identify appropriate DCIS patients for long-term active surveillance while avoiding surgery Early results show excellent tolerability and steady enrollment, with many patients electing to continue active surveillance, suggesting feasibility of this patient-centered "window of opportunity" approach Future work focuses on integrating imaging and molecular biomarkers to refine prediction of progression risk, guide personalized care pathways, improve patient experience and quality of life, and assess long-term outcomes including durability of active surveillance and invasive recurrence Low dose (Z)-endoxifen in the I-SPY2 Endocrine Optimization Pilot Clinical significance The excellent tolerability and biologic activity of low-dose (Z)-endoxifen, demonstrated by reductions in Ki-67, MRI tumor volume, and ctDNA, support its potential as an effective neoadjuvant endocrine therapy for HR+/HER2- early breast cancer and justifies dose escalation and combination strategies to further improve patient outcomes Key takeaways The daily 10 mg (Z)-endoxifen dose was well tolerated, with 95% of patients completing ≥75% of therapy and low-grade side effects, demonstrating strong feasibility in an endocrine-naïve HR+/HER2- population Biologic activity was evident, with meaningful reductions in Ki-67, MRI functional tumor volume (–72% median), and ctDNA clearance observed in 70% of patients who were initially ctDNA-positive, indicating endocrine responsiveness Clinical impact was modest but supportive, with one mPEPI-0 outcome; the program is now escalating to 40 mg/day (targeting both ERα and PKCβ1) with or without abemaciclib to further optimize neoadjuvant endocrine therapy (Z)-Endoxifen Maintains ERα Antagonist Function Against ESR1 Mutants via Inactive Conformation Stabilization and Reversal of Mutant ESR1-Associated Transcriptional Signatures Clinical significance Findings demonstrate (Z)-endoxifen as a promising therapeutic option for patients with ER+/ESR1 mutant breast cancer, a population with limited effective endocrine treatments and high unmet need Key Takeaways (Z)-Endoxifen shown to maintain potent ERα antagonist activity across key ESR1 mutations (Y537S, D538G) by stabilizing inactive receptor conformations, with computational, energetic, and metadynamics analyses showing ESR1 mutants still retain antagonist-compatible states Functional assays confirmed strong suppression of ER signaling in both wild-type and mutant ESR1 backgrounds, demonstrating robust inhibitory activity even under estrogen-rich conditions and validating the mechanistic modeling findings Transcriptomic analyses showed that (Z)-endoxifen reverses multiple mutant ESR1–associated oncogenic pathways (e.g., estrogen response, E2F, Myc) while restoring beneficial programs (oxidative phosphorylation, p53), highlighting its therapeutic potential for ER+ / ESR1 mutant breast cancer A Randomized Phase 2 Non-Inferiority Trial of (Z)-Endoxifen + Goserelin vs Exemestane + Goserelin as a Neoadjuvant Treatment for Premenopausal Women with ER+/HER2- Breast Cancer (EVANGELINE) Clinical Significance (Z)-endoxifen with Ovarian Function Suppression (OFS) may offer a more tolerable and biologically potent alternative to aromatase-inhibitor (AI)-based regimens for premenopausal ER+/HER2– patients, potentially expanding endocrine therapy options and improving adherence while maintaining robust neoadjuvant efficacy Key Takeaways EVANGELINE is the first trial to evaluate (Z)-endoxifen with OFS as a neoadjuvant therapy for patients with premenopausal ER+/HER2– breast cancer, addressing a major unmet need for patients who cannot tolerate AI with OFS therapy Pharmacodynamic run-in data showed strong early biologic activity, with 86% of patients achieving a Week 4 Ki-67 ≤10%, supporting the selection of 40 mg (Z)-endoxifen with OFS for Phase II, and demonstrating promising antiproliferative efficacy The study design incorporates a Simon two-stage approach to test whether (Z)-endoxifen with OFS can meet or exceed a 65% Ki-67 response threshold, with secondary endpoints including safety, RCB, PEPI score, and MRI-based tumor response About Atossa Therapeutics Atossa Therapeutics, Inc. (Nasdaq: ATOS) is a clinical-stage biopharmaceutical company developing innovative medicines in oncology and other areas of significant unmet need. The Company's lead product candidate, (Z)-endoxifen, is currently in development across several clinical settings. 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 and refer to Atossa's filings with the U.S. Securities and Exchange Commission (SEC). Forward-Looking Statements This press release contains certain "forward-looking statements" within the meaning of applicable securities laws, including but not limited to, our expectations regarding the Company's development and regulatory strategy and related milestones, the potential indications that the Company may pursue for (Z)-Endoxifen, the potential for (Z)-Endoxifen to receive regulatory approval and the timing thereof, expectations regarding the design, enrollment, data, timing, results and outcomes of the Company's clinical studies, and the potential market and growth opportunities for the Company. Words such as "expect," "potential," "continue," "may," "will," "should," "could," "would," "seek," "intend," "plan," "estimate," "anticipate," "believe," "design," "predict," "future," or other similar expressions or statements regarding intent, belief or current expectations, are forward-looking statements. Forward-looking statements in this press release are subject to risks and uncertainties that may cause actual results, outcomes, or the timing of actual results or outcomes to differ materially from those projected or anticipated, including, without limitation, risks and uncertainties associated with: our ability to successfully execute our strategy to shorten our clinical development timelines and pursue a metastatic breast cancer indication, DMD indication or other indications for our lead program, (Z)-Endoxifen; expected timing, completion and results of our preclinical studies, clinical trials and research and development programs; the unpredictable relationship between preclinical study results and clinical study results; the timing or likelihood of regulatory filings and approvals; the outcome or timing of necessary regulatory approvals; our ability to regain and maintain compliance with Nasdaq listing requirements; our ability to establish and maintain intellectual property rights covering our products; the impact of general macroeconomic conditions on our business; our ability to raise capital; and other risks and uncertainties detailed from time to time in Atossa's filings with the SEC, including, without limitation, its Annual Reports on Form 10-K and Quarterly Reports on Form 10-Q. Forward-looking statements are presented as of the date of this press release. Except as required by law, we do not intend to update any forward-looking statements. SOURCE Atossa Therapeutics Inc 21% more press release views with Request a Demo

Designation expands (Z)-Endoxifen program into rare pediatric neuromuscular disease and may qualify Atossa for a future Priority Review Voucher upon approval SEATTLE, Dec. 11, 2025 /PRNewswire/ -- Atossa Therapeutics, Inc. (Nasdaq: ATOS) ("Atossa" or the "Company"), a clinical-stage biopharmaceutical company developing novel therapies in oncology and other areas of high unmet clinical need, today announced that the U.S. Food and Drug Administration ("FDA") has granted Rare Pediatric Disease ("RPD") designation to (Z)-Endoxifen for the treatment of Duchenne Muscular Dystrophy ("DMD"). RPD designation is granted to drug candidates intended to treat serious or life-threatening diseases that primarily affect individuals from birth to 18 years of age. Upon approval of a qualifying marketing application, drugs with RPD designation may be eligible for a Priority Review Voucher ("PRV"), which can be used to obtain priority review for a future application or may be sold or transferred to another sponsor. In the last 18–24 months, disclosed PRV sales have ranged from $100–$160 million. "This designation is an important regulatory milestone for Atossa, and we believe a strong validation of the science supporting the potential of (Z)-Endoxifen as a treatment for Duchenne Muscular Dystrophy," said Steven Quay, M.D., Ph.D., Atossa Therapeutics President and Chief Executive Officer. "DMD is one of the most devastating childhood diseases. Families urgently need better options beyond steroids and gene-targeted approaches. While oncology remains our core focus, this milestone highlights (Z)-Endoxifen's potential as a platform therapy in both cancer and rare diseases, opening the door to potential non-dilutive value creation through the Rare Pediatric Disease program." "RPD designation provides a regulatory framework and an enhanced level of interaction with the FDA as we define the clinical development path in DMD," said Janet Rea, MSPH, Senior Vice President of Research and Development at Atossa. "We are very encouraged by emerging preclinical data and by (Z)-Endoxifen's potential to be a differentiated mechanism as a potent SERM/D, and look forward to our planned advancement of this program to the clinic for boys living with DMD. Unlike more recent therapeutic approaches, (Z)-Endoxifen does not target specific exon defects, thus potentially offering a broader and more accessible treatment approach for this patient population. Having previously secured IND clearance for what is now the DMD treatment, Exondys 51® (eteplirsen), I am excited to further Atossa's DMD (Z)-Endoxifen program." About Rare Pediatric Disease Designation The FDA's Rare Pediatric Disease designation is reserved for serious or life-threatening diseases that primarily affect individuals from birth to 18 years old and that meet the definition of a rare disease or condition within the meaning of Section 526 of the Federal Food, Drug & Cosmetic Act ("FD&C Act"). Currently, the FDA may not award any new rare pediatric disease PRVs unless the application is (i) for a drug that is designated as a drug for a rare pediatric disease not later than December 20, 2024, and (ii) is approved under the program not later than September 30, 2026. The House has passed the Mikaela Naylon "Give Kids a Chance Act" to extend voucher-award authority to 2029, with retroactive effect, and the bill is now pending Senate action. Assuming the program is renewed, drugs granted RPD designation may be eligible for a PRV upon FDA approval of a qualifying New Drug Application or Biologics License Application, provided it meets all statutory criteria under Section 529(a)(4) of the FD&C Act. A PRV may be used by the sponsor or sold or transferred to another company. About Duchenne Muscular Dystrophy Duchenne Muscular Dystrophy is a rare, progressive, X-linked neuromuscular disorder caused by mutations in the dystrophin gene. Symptoms typically emerge in early childhood and include progressive muscle weakness, loss of ambulation, respiratory compromise, and cardiomyopathy. DMD is uniformly fatal, often in early adulthood, and despite recent therapeutic advances, there remains a substantial unmet medical need for safe, effective, and accessible treatments. About (Z)-Endoxifen (Z)-Endoxifen is a potent Selective Estrogen Receptor Modulator/Degrader (SERM/D) with demonstrated activity across multiple mechanisms of interest. Atossa is evaluating its potential applications in oncology and rare diseases. The Company's proprietary oral formulation has shown a favorable safety profile and pharmacology distinct from tamoxifen, including ER-targeted effects and PKC inhibition. Atossa's (Z)-Endoxifen is not approved for any indication. Atossa's (Z)-Endoxifen program is supported by a growing global intellectual property portfolio, including multiple recently issued U.S. patents and numerous pending applications worldwide. About Atossa Therapeutics Atossa Therapeutics, Inc. (Nasdaq: ATOS) is a clinical-stage biopharmaceutical company developing innovative medicines in oncology and other areas of significant unmet need. The Company's lead product candidate, (Z)-Endoxifen, is currently in development across several clinical settings. More information is available at . Forward-Looking Statements This press release contains certain "forward-looking statements" within the meaning of applicable securities laws, including but not limited to, our expectations regarding the Company's development and regulatory strategy and related milestones, the potential indications that the Company may pursue for (Z)-Endoxifen, the potential for (Z)-Endoxifen to receive regulatory approval and the timing thereof, the potential extension of the RPD Priority Review Voucher program and the Company's potential eligibility for and value of a future Priority Review Voucher, and the potential market and growth opportunities for the Company. Words such as "expect," "potential," "continue," "may," "will," "should," "could," "would," "seek," "intend," "plan," "estimate," "anticipate," "believe," "design," "predict," "future," or other similar expressions or statements regarding intent, belief or current expectations, are forward-looking statements. Forward-looking statements in this press release are subject to risks and uncertainties that may cause actual results, outcomes, or the timing of actual results or outcomes to differ materially from those projected or anticipated, including, without limitation, risks and uncertainties associated with: our ability to successfully execute our strategy to shorten our clinical development timelines and pursue a metastatic breast cancer indication, DMD indication or other indications for our lead program, (Z)-Endoxifen; expected timing, completion and results of our preclinical studies, clinical trials and research and development programs; the unpredictable relationship between preclinical study results and clinical study results; the timing or likelihood of regulatory filings and approvals; the outcome or timing of necessary regulatory approvals; our ability to receive a Priority Review Voucher for (Z)-Endoxifen, if approved, which is subject to, among other factors, the U.S. federal government's extension of the RPD PRV program and such extension being effective retroactively; our ability to regain and maintain compliance with Nasdaq listing requirements; our ability to establish and maintain intellectual property rights covering our products; the impact of general macroeconomic conditions on our business; our ability to raise capital; and other risks and uncertainties detailed from time to time in Atossa's filings with the SEC, including, without limitation, its Annual Reports on Form 10-K and Quarterly Reports on Form 10-Q. The market value of a Priority Review Voucher is variable and subject to a number of factors beyond our control and reported past PRV sale amounts are not necessarily indicative of PRV sale amounts in the future. Forward-looking statements are presented as of the date of this press release. Except as required by law, we do not intend to update any forward-looking statements. SOURCE Atossa Therapeutics Inc 21% more press release views with Request a Demo