Atossa Therapeutics reports results from Phase 2 EOP sub-study

Atossa Therapeutics (ATOS) reported full results from the Phase 2 Endocrine Optimization Pilot, or EOP, sub-study within the I-SPY2 TRIAL evaluating low-dose oral Z-endoxifen as a neoadjuvant treatment in 20 women with stageII/III estrogen-receptor-positive, HER2-negative breast cancer. Key Findings: Primary feasibility goal surpassed -95% of participants completed at least 75percent of planned dosing, far exceeding the predefined 75% threshold. Early anti-proliferative activity -Median Ki-67 fell from 10.5% at baseline to 5percent by Week3: 65% of patients achieved Ki-67less than or equal to10% at that time point, and suppression was maintained at surgery. Robust imaging response -Median functional tumor volume measurement decreased 77.7% from baseline to surgery, and the longest tumor diameter from baseline to preoperative MRI was reduced by 36.8%. Well-tolerated safety profile -Adverse events were predominantly Grade1; vasomotor symptoms and fatigue were most common. Only three Grade3 events occurred in a single patient and were deemed unrelated to study drug; no Grade4 or Grade5 events were reported. No participants achieved a pathologic complete response, and residual cancer burden classes skewed toward RCB-II/III, indicating moderate to extensive residual disease. Atossa is actively enrolling participants into an additional I-SPY2 cohort testing Z-endoxifen at a 40 mg daily dose and in combination with abemaciclib, with and without ovarian function suppression. Top-line data from these arms are expected beginning in 2026.