- Atossa Therapeutics (ATOS, Financial) completes Phase 2 trial with 95% compliance in dosing.
- 77.7% median reduction in tumor volume observed.
- Planned higher-dose studies underway; data expected in 2026.
Atossa Therapeutics (ATOS), a clinical-stage biopharmaceutical company, revealed full results from its Phase 2 Endocrine Optimization Pilot sub-study within the I-SPY 2 TRIAL. This study assessed the efficacy of low-dose oral (Z)-endoxifen, a treatment designed for stage II/III ER+, HER2-negative breast cancer. The sub-study successfully met its primary feasibility goal with 95% of participants completing at least 75% of the planned dosing regimen.
Most notably, the trial recorded a significant reduction in cancer markers, with the median Ki-67 proliferation marker dropping from 10.5% to 5% by the third week. Additionally, there was a median 77.7% decrease in functional tumor volume, indicating robust efficacy of the treatment.
Despite these positive indicators, no participants achieved a pathologic complete response (pCR), which was anticipated due to the deliberately low 10mg dosing aimed at evaluating safety and initial efficacy. The safety profile of (Z)-endoxifen remained favorable, with most reported adverse events being Grade 1, such as hot flushes and fatigue, and no serious adverse events attributed to the drug.
With the initial trial laying the groundwork, Atossa is now enrolling participants for new I-SPY 2 cohorts, which will explore higher doses of (Z)-endoxifen (40mg daily). These trials are set to evaluate the enhanced efficacy of endoxifen in combination with abemaciclib, a CDK4/6 inhibitor, with top-line results expected in 2026.
