Atossa Therapeutics to pursue metastatic breast cancer for (Z)-endoxifen

Atossa Therapeutics (ATOS) announced its strategic decision to pursue a metastatic breast cancer indication for (Z)-endoxifen. Atossa believes that pursuing a metastatic indication may offer a more efficient regulatory pathway to deliver (Z)-endoxifen to women in urgent need, and simultaneously plans to work with the FDA to advance additional indications, such as breast cancer prevention and neoadjuvant therapy, that often require larger and longer clinical trials. (Z)-endoxifen has shown encouraging results in early-stage trials, which we believe reinforces its potential as a transformative therapy for breast cancer. Key findings from early clinical programs include: Significantly improved progression-free survival in CDK4/6i-naive patients: (Z)-endoxifen more than doubled the median PFS compared to tamoxifen highlighting its potency in an endocrine-sensitive population. Substantial activity observed even after tamoxifen progression: Patients in the crossover arm who progressed on tamoxifen and switched to (Z)-endoxifen experienced clinical benefit, including partial responses and prolonged stable disease exceeding 2-3 years in some cases. Favorable safety profile: Despite its higher potency, (Z)-endoxifen has not shown unexpected safety concerns beyond what is typically seen with tamoxifen and has been generally well-tolerated. The company said, “We believe that pursuing an initial approval in metastatic breast cancer provides an efficient regulatory and clinical path to market, potentially allowing Atossa to more rapidly bring (Z)-endoxifen to patients who need it most. This approach can also strengthen the foundation for the expansion of (Z)-endoxifen into earlier-stage disease settings, where (Z)-endoxifen has already shown significant promise in reducing tumor proliferation and preventing recurrence. Beyond metastatic disease, Atossa remains committed to demonstrating the broad clinical utility of (Z)-endoxifen across the breast cancer treatment paradigm. Since the release of compelling data at the end of 2024, the Company is actively engaging with the FDA to further define a regulatory path forward for additional indications, including in: Breast Cancer Prevention: Prior studies have indicated that (Z)-endoxifen can significantly reduce breast tissue density and estrogen receptor activity, key risk factors for developing breast cancer. Neoadjuvant Therapy: Data from early-stage patients indicate that the 4-week Ki-67 less than or equal to10% response rate remained consistently above 85 percent across all dose levels, regardless of the presence of ovarian function. These findings suggest that (Z)-endoxifen may effectively reduce tumor proliferation, which may lead to improved surgical outcomes and long-term prognosis. Atossa Therapeutics remains dedicated to accelerating the development of (Z)-endoxifen with the goal of helping patients across all stages of breast cancer to benefit from its therapeutic potential.”