Atossa Therapeutics Announces Positive Interim Phase 2 Data from Endoxifen Breast Cancer Treatment

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Atossa Therapeutics Announces Positive Interim Phase 2 Data from Endoxifen Breast Cancer Treatment

SEATTLE, May 07, 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, today announced positive interim results from its Phase 2 study of oral Endoxifen to treat breast cancer in the window of opportunity between diagnosis of breast cancer and surgery. A statistically significant (p = 0.031) reduction of about 74% in tumor cell proliferation was achieved over the 22 days of dosing. Proliferation was measured by Ki-67, a recognized standard measurement of breast cancer cell proliferation.

Window of Opportunity Phase 2 Study Interim Results

The purpose of this study is to determine if Atossa’s oral Endoxifen reduces breast cancer tumor cell proliferation as measured by several biomarkers, including Ki-67. The open-label study was designed to permit an interim analysis of the Ki-67 change. The requirement was to achieve a meaningful Ki-67 change in at least two of eight patients. All patients (N=6) experienced a significant reduction in Ki-67. 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. In a paper entitled, “Prognostic value of different cut-off levels of Ki-67 in breast cancer: a systematic review and meta-analysis of 64,196 patients,” Ki-67 was an independent prognostic value for predicting overall survival in ER+ breast cancer patients. 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.

“These are the most significant and exciting results achieved in any of our Endoxifen clinical studies to date,” commented Steven C. Quay, Ph.D., M.D., Atossa’s CEO and President. “In designing the study, we had hoped that we could reduce tumor cell proliferation in at least two out of the first eight patients. The results surpassed our expectations with a substantial reduction in tumor cell activity in every one of the six patients treated. This has the potential to validate the role of Endoxifen in reducing tumor proliferation between diagnosis and surgery. We are evaluating the role that Endoxifen therapy in the window of opportunity might play in helping some patients avoid or defer surgery, improving surgical outcomes by avoiding mastectomy and improving cosmetic results, and potentially replacing other pre-surgical chemotherapies or endocrine therapies with Endoxifen.”

“I have been very impressed with the rapid impact Endoxifen has had on tumor proliferation in these patients in the neoadjuvant setting and also the absence of certain side effects, like hot flashes,” commented Vinod Ganju, MBBS, FRACP, principal investigator. “It is my pleasure to be playing a role in developing a much-needed therapy that could improve outcomes for breast cancer patients. Given the results to date, we are interested in expanding the use of Endoxifen to other clinical settings, for example, to metastatic breast cancer patients.”

Results of the study are consistent with the results in a recent compassionate use, or expanded access, single-patient study with oral Endoxifen. At the end of 2018, the FDA approved a single patient IND for a breast cancer patient to receive our oral Endoxifen in the window of opportunity. That patient experienced a 50% reduction in Ki-67 after taking daily doses for 20 days prior to her surgery. Based on these results, an additional compassionate use approval was granted by the FDA for the same patient, who has continued to take oral Endoxifen for over a year in the adjuvant setting following her surgery. 

Based on these positive results, Atossa is continuing to enroll the remaining 19 patients in the study and will then seek regulatory approval to move into a Phase 3 study.

About the Endoxifen Window of Opportunity Phase 2 Study

Atossa’s Phase 2 study of its oral Endoxifen in the window of opportunity between diagnosis of breast cancer and surgery is being conducted in Australia. 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 to determine if the administration of oral Endoxifen reduces the 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.

About Window of Opportunity Therapy

The goal of pharmaceutical treatment in patients with non-metastatic breast cancer after surgery (also called adjuvant therapy), for example by chemotherapy or hormone therapy, is typically to reduce the risk of the cancer recurring. Administering therapy in the window of opportunity prior to surgery (also called neoadjuvant therapy) may also reduce the risk of recurrence; however, the primary goal in this setting is typically to downstage the tumor and provide information regarding treatment response. Downstaging the tumor may convert a large, inoperable tumor in selected frail patients into an operable tumor that may allow breast conserving surgery in place of mastectomy. This may also improve cosmetic outcomes, and reduce postoperative complications such as lymphedema. Successful neoadjuvant therapy may allow some patients to avoid surgery altogether or defer surgery under a “watch and wait” strategy. The results of neoadjuvant therapy may also be used to guide adjuvant treatment recommendations as the therapy can provide the opportunity to obtain imaging studies, tumor specimens, and blood samples prior to and after the neoadjuvant treatment, which may assist in the identification of tumor or patient specific adjuvant therapies.

Based on these strong study results, Atossa will be 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. Reduction in Ki-67 in and of itself may not, however, be an indication that the FDA or other regulatory authorities will approve. Atossa plans to seek input from regulatory authorities about potential approvable indications for Endoxifen in the window of opportunity and the design of future clinical studies. 

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, actions and inactions by the FDA, the outcome or timing of regulatory approvals needed by Atossa including those needed to commence studies such as the COVID-19 HOPE Study, 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 Ki-67 or any other result from a neoadjuvant study is an approvable endpoint for oral Endoxifen, 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.

Atossa Therapeutics Company Contact:

Atossa Therapeutics, Inc.
Kyle Guse
CFO and General Counsel
(O) 800-351-3902

Investor Relations Contact:

Office: 516.222.2560

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May 07, 2020