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Atossa Therapeutics Announces Interim Findings Following 18 Months Expanded Access Single-Patient Study of Atossa’s Endoxifen In Breast Cancer

By John F. Heerdink, Jr.

Thursday, July 30th, 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, announced 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 were reported to 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. 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,” stated Steve Quay, Ph.D., M.D., Atossa’s President, and CEO.

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.


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 the 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 the use of Endoxifen in place of other neoadjuvant therapies such as chemotherapy, aromatase inhibitors and other endocrine therapies like tamoxifen.


Atossa’s shares have been on an upward trend this year after touching a low of $.76/share during the market selloff in Q1 2020 as they spiked to a 52-week high of $4.87/share on Thursday before closing at $3.98/share.

Please visit the Atossa Therapeutics (ATOS) page at Vista Partners to keep up with their progress and to learn more daily about their work and developments.

You may want to also read the following story: 

Atossa Therapeutics Announced Successful In Vitro Testing Of Its COVID-19 Nasal Spray Formulation Treatment Candidate


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