Atossa Therapeutics Announces Findings from FDA-Approved Expanded Access Treatment with Endoxifen

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Atossa Therapeutics Announces Findings from FDA-Approved Expanded Access Treatment with Endoxifen
Patient has taken Atossa’s Endoxifen for 18 months without side effects and without cancer recurrence

SEATTLE, July 30, 2020 (GLOBE NEWSWIRE) — Atossa Therapeutics, Inc. (Nasdaq: ATOS), a clinical-stage biopharmaceutical company seeking to discover and develop innovative medicines in areas of significant unmet medical need with a current focus on breast cancer and COVID-19, announces interim findings following 18 months of an Expanded Access (or “compassionate use”) single-patient study of Atossa’s Endoxifen. To date, the patient has not had a recurrence of breast cancer, as assessed by clinical breast examination and mammography; has not had treatment-related changes in periodic laboratory blood tests and general clinical examinations; and the treatment has been well tolerated, including an absence of typically seen vasomotor symptoms (for example, night sweats and hot flashes).

The study results show that treatment with Atossa’s proprietary Endoxifen for 20 days prior to unilateral mastectomy and for 18 months after surgery as an adjuvant did not lead to vasomotor symptoms commonly associated with tamoxifen, an FDA-approved drug frequently prescribed for breast cancer treatment. Endoxifen did not cause other safety and tolerability concerns in this patient. The percentage of cells expressing ER+ or Ki-67 decreased from the initial biopsy to the biopsy on the day of surgery (a 50% reduction in the case of Ki-67 and a 22% decrease in ER+ cells); plasma Endoxifen reached the potential therapeutic level (= 35 nM) by day 6; and steady state Endoxifen was maintained through day 20 prior to surgery. Atossa plans to publish a manuscript of the case study.

“Pre-menopausal breast cancer patients have very limited treatment options,” commented Steve Quay, Ph.D., M.D., Atossa’s President and CEO. “They are often reluctant to take tamoxifen because most patients experience hot flashes and night sweats. Moreover, many patients, including the patient here, lack the proper liver enzymes to metabolize tamoxifen so they may not receive a therapeutic benefit. We look forward to continuing enrollment in our Phase 2 study in this ‘window of opportunity’ setting and to continuing to follow this patient’s progress.”

At the end of 2018, the FDA authorized a single-patient study under its Expanded Access, or compassionate use program, for this breast cancer patient to receive Atossa’s oral Endoxifen in the “window of opportunity” between diagnosis of breast cancer and surgery. Following surgery, an additional compassionate use authorization was granted by the FDA for the same patient, who has now continued to take oral Endoxifen for approximately 18 months in the adjuvant setting following her surgery. She will continue to take oral Endoxifen daily under this authorization.

Atossa’s Ongoing Phase 2 Window of Opportunity Study of Endoxifen

In addition to the compassionate use patient, Atossa is conducting a Phase 2 study of its oral Endoxifen in the window of opportunity between diagnosis of breast cancer and surgery. The study will enroll up to 25 newly-diagnosed patients with ER+ and human epidermal growth factor receptor 2 negative (HER2-) stage 1 or 2 invasive breast cancer, requiring mastectomy or lumpectomy. Patients receive Atossa’s proprietary oral Endoxifen for at least 14 days from the time of diagnosis up to the day of surgery. The primary endpoint is reduction of tumor activity as measured by Ki-67. The secondary endpoints are safety and tolerability and assessment of the study drug on expression levels of both estrogen and progesterone receptors. The impact on additional markers of cellular activity will also be explored. The Phase 2 study is being conducted on behalf of Atossa by Avance Clinical, which successfully completed four Phase 1 studies of Atossa’s Endoxifen.

The open-label study is designed to permit an interim analysis of the Ki-67 change. The requirement to proceed with the study was to achieve a meaningful Ki-67 change in at least two of eight patients. Impressively, all patients in the interim group (N=6) have experienced a significant reduction in Ki-67. As previously announced, a summary of these results includes:

  • Ki-67 was reduced by more than 50% in every patient in the window of opportunity between initial biopsy and surgery, with an overall reduction of 74%.
  • All six patients had a Ki-67 below 25% after treatment. A meta-analysis of 64,196 patients found that Ki-67 was an independent prognostic value for predicting overall survival in ER+ breast cancer patients (Petrelli, F., Viale, G., Cabiddu, M. et al. Prognostic value of different cut-off levels of Ki-67 in breast cancer: a systematic review and meta-analysis of 64,196 patients. Breast Cancer Res Treat 153, 477-491 (2015) Ki-67 levels below 25% were associated with the lowest risk of death in this systematic review and meta-analysis.
  • Treatment ranged from 16-40 days with an average of 22 days.
  • There were no safety or tolerability issues, including vasomotor symptoms such as hot flashes and night sweats, which are often a tolerability challenge for patients on tamoxifen.

Based on interim results from the window of opportunity study and the results from the compassionate use patient, Atossa is evaluating a number of potential clinical benefits and potential indications for its oral Endoxifen in the window of opportunity setting. These may include avoidance of surgery in some patients, such as older and/or frail patients, allowing for breast conservation surgery, and use of Endoxifen in place of other neoadjuvant therapies such as chemotherapy, aromatase inhibitors and other endocrine therapies like tamoxifen.

About Atossa Therapeutics

Atossa Therapeutics, Inc. is a clinical-stage biopharmaceutical company seeking to discover and develop innovative medicines in areas of significant unmet medical need with a current focus on breast cancer and COVID-19. For more information, please visit

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, whether in vitro test results will also be achieved in in vivo studies, including human clinical studies, actions by and interactions with the FDA, the outcome or timing of regulatory approvals needed by Atossa including those needed to commence human clinical studies of COVID-19 therapies, 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, 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.

Company Contact:
Atossa Therapeutics, Inc.
Kyle Guse, CFO and General Counsel
Office: 866 893-4927

Investor Relations Contact:
Core IR
Office:(516) 222-2560

Source: Atossa Therapeutics, Inc.

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Jul 30, 2020