---
schema_version: "secwatch.filing_event.v1"
accession: "0001193125-26-003506"
form_type: "8-K"
ticker: "ATOS"
cik: "0001488039"
company_name: "ATOSSA THERAPEUTICS, INC."
filed_at: "2026-01-06T23:59:59+00:00"
generated_at: "2026-05-16T11:31:47.527466+00:00"
event_type: "regulatory"
sentiment: "positive"
materiality_score: 0.65
calibrated_materiality_score: 0.65
confidence: "high"
source: SEC EDGAR
---

# Atossa Therapeutics receives FDA 'Study May Proceed' letter for (Z)-Endoxifen metastatic breast cancer trial

## Summary
- FDA issued 'Study May Proceed' letter for Atossa's IND for (Z)-Endoxifen in metastatic ER+/HER2- breast cancer.
- Trial will evaluate (Z)-Endoxifen in tumors resistant to other endocrine therapies; targets PKCβ1 pathway.
- CEO Dr. Steven Quay calls this an important regulatory milestone to expand (Z)-Endoxifen's potential use.
- (Z)-Endoxifen is a potent SERM/D with distinct pharmacology from tamoxifen; not yet approved for any indication.
- Program backed by growing global IP portfolio including issued U.S. patents and pending applications.

## SEC filing metadata
- accession: 0001193125-26-003506
- form_type: 8-K
- ticker: ATOS
- cik: 0001488039
- company_name: ATOSSA THERAPEUTICS, INC.
- filed_at: 2026-01-06T23:59:59+00:00
- event_type: regulatory
- sentiment: positive
- materiality_score: 0.65
- calibrated_materiality_score: 0.65
- confidence: high
- sec_items: 8.01, 9.01
- EDGAR index: https://www.sec.gov/Archives/edgar/data/1488039/000119312526003506/0001193125-26-003506-index.htm
- EDGAR primary document: https://www.sec.gov/Archives/edgar/data/1488039/000119312526003506/atos-20260106.htm

## Machine-readable alternates
- HTML: https://secwatch.observer/filing/0001193125-26-003506
- JSON: https://secwatch.observer/filing/0001193125-26-003506.json
- Plain text: https://secwatch.observer/filing/0001193125-26-003506.txt

This AI-assisted summary is a reading aid. Review the linked SEC EDGAR filing before relying on any specific claim.