Atossa Therapeutics, Inc. (Nasdaq: ATOS), a clinical-stage biopharmaceutical company seeking to develop innovative medicines in areas of significant unmet medical need in oncology with a current focus on breast cancer, announced today that the U.S. Food and Drug Administration (FDA) has lifted the clinical hold and authorized initiation of its Phase 2 neoadjuvant clinical study of (Z)-endoxifen in premenopausal women with early-stage estrogen receptor positive (ER+) and human epidermal growth factor receptor 2 negative (HER2-) breast cancer. This is the first study of Atossa’s proprietary (Z)-endoxifen in the United States.

At this time, Atossa also announced that it is discontinuing its COVID-19 program (AT-301) so that it can refocus resources on this critical study in breast cancer.

“Continuing the development of our proprietary (Z)-endoxifen here in the United States has been a key goal which builds on the recent issuance of a U.S. patent for our proprietary (Z)-endoxifen and results from our Phase 2 “window-of-opportunity” study in Australia,” commented Steven Quay, M.D., Ph.D., Atossa’s CEO, Chairman and President. “We are excited to have engaged Dr. Matthew Goetz, the Erivan K. Haub Family Professor of Cancer Research Honoring Richard F. Emslander, M.D. at Mayo Clinic and Director of the Mayo Clinic Breast Cancer SPORE, as the lead principal investigator for this multi-center study. We look forward to opening the study in the fourth quarter.”

About the Study

The study, “A Randomized Phase 2 Noninferiority Trial of (Z)-endoxifen and Exemestane + Goserelin as Neoadjuvant Treatment in Premenopausal Women with ER+/HER2- Breast Cancer”, or also known as “EVANGELINE,” is an open-label, randomized, Phase 2 study designed to investigate (Z)-endoxifen for the neoadjuvant treatment of premenopausal women ages 18 and older with early stage (Grade 1 or 2) ER+/HER2- breast cancer. InClin Inc., a full-service Contract Research Organization, has been contracted to execute this study.

This study is a multicenter (approximately 25 sites) study in United States and will enroll about 175 patients and is designed with two cohorts: a PK Run-In Cohort to investigate pharmacokinetics and identify a dose for the Treatment Cohort and a Treatment Cohort to investigate the safety and efficacy of (Z)-endoxifen compared with a prospective control (exemestane + goserelin, two drugs often used in combination to treat this patient population).

The primary objective of the study is to assess whether the endocrine sensitive disease rate at 4 weeks with (Z)-endoxifen is non-inferior to exemestane plus goserelin in premenopausal women with ER+/HER2- breast cancer. Endocrine sensitivity, or the effect of endocrine therapy on the tumor, will be measured by Ki-67%, a biomarker for tumor cell proliferation. Ki-67 is known to be prognostic for 5-year disease-free survival in the neoadjuvant endocrine treatment of ER+/HER2- breast cancer. The neoadjuvant setting of this study will allow Atossa to investigate several translational endpoints using paired tumor samples.

Patients will be enrolled with the intent of surgical treatment in the involved breast(s) after completing neoadjuvant study treatment. Patients will receive neoadjuvant study treatment for up to six months. Surgery will be performed within seven days of the last dose of study treatment.

About Premenopausal Patients with ER+/HER2- Breast Cancer

Breast cancer is the most frequently diagnosed cancer in premenopausal women worldwide. It is estimated that almost half of the cancers that occur in women aged 15-49 is breast cancer. An overwhelming majority (75%) of premenopausal breast cancer falls under luminal A (ER+/HER2-) or B (ER+/HER2+) subtypes. Ovarian function suppression, when combined with either tamoxifen or an aromatase inhibitor, is the standard of care for the endocrine management of premenopausal ER+/HER2- breast cancer.

About (Z)-Endoxifen

(Z)-endoxifen is the most active metabolite of the FDA approved Selective Estrogen Receptor Modulator (SERM), tamoxifen. Studies by others have demonstrated that the anti-estrogenic effects of tamoxifen are driven in a concentration-dependent manner by (Z)-endoxifen. In addition to its anti-estrogen effects, (Z)-endoxifen at higher concentrations has been shown to target PKCβ1, a known oncogenic protein. 

Atossa has developed a proprietary oral formulation of (Z)-endoxifen that does not require liver metabolism to achieve therapeutic concentrations and is encapsulated to bypass the stomach as acidic conditions may render (Z)-endoxifen inactive. Atossa’s (Z)-endoxifen has been shown to be well tolerated in Phase 1 studies and in a small Phase 2 study of women with breast cancer. We currently are studying our (Z)-endoxifen in healthy women with measurable breast density and premenopausal women with ER+/HER2- breast cancer.

Atossa has been issued U.S. Patent No. 11,261,151, titled “Methods for Making and Using Endoxifen” which is directed to compositions of storage-stable (Z)-endoxifen and methods of treating hormone-dependent breast disorders using the storage-stable (Z)-endoxifen. This patent is not expected to expire until 2038.

Update on Ongoing Phase 2 Study of (Z)-Endoxifen Phase 2 Study in Stockholm

The Company has continued to make steady progress with its ongoing study of (Z)-endoxifen in premenopausal women with measurable breast density in Stockholm, Sweden. It has now enrolled approximately 40% of the subjects in that study, which puts Atossa on track to completing enrollment of all 240 participants in the second half of 2023.

About Atossa Therapeutics

Atossa Therapeutics, Inc. is a clinical-stage biopharmaceutical company seeking to develop innovative medicines in areas of significant unmet medical need in oncology with a current focus on breast cancer.

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Forward Looking Statements

Forward-looking statements in this press release, which Atossa undertakes no obligation to update, are subject to risks and uncertainties that may cause actual results to differ materially from the anticipated or estimated future results, including the risks and uncertainties associated with any variation between interim and final clinical results, actions and inactions by the FDA, the outcome or timing of regulatory approvals needed by Atossa including those needed to commence studies of AT-H201 and (Z)-endoxifen, lower than anticipated rate of patient enrollment, estimated market size of drugs under development, the safety and efficacy of Atossa’s products, performance of clinical research organizations and investigators, obstacles resulting from proprietary rights held by others such as patent rights, whether reduction in breast density or in Ki-67 or any other result from a neoadjuvant study is an approvable endpoint for (Z)-endoxifen, whether Atossa can complete acquisitions, and other risks detailed from time to time in Atossa’s filings with the Securities and Exchange Commission, including without limitation its periodic reports on Form 10-K and 10-Q, each as amended and supplemented from time to time.

Contact:Atossa Therapeutics, Inc.Kyle Guse, General Counsel and Chief Financial

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