Puma Biotechnology, Inc. (NASDAQ: PBYI), a biopharmaceutical company (the Company), has been notified by the U.S. Food and Drug Administration (FDA) that its Investigational New Drug Application (IND) submission has been reviewed, and Puma can proceed with the clinical development of alisertib for the treatment of patients with human epidermal growth factor receptor 2-negative (HER2-negative), hormone receptor-positive metastatic breast cancer in Puma’s Phase II ALISCA-Breast1 trial (Study PUMA-ALI-4201). This trial will investigate alisertib in combination with endocrine treatment (consisting of either anastrozole, exemestane, letrozole, fulvestrant or tamoxifen) in chemotherapy-naïve patients with hormone receptor-positive, HER2-negative recurrent or metastatic breast cancer. Patients must have been previously treated with CDK 4/6 inhibitors and received at least two prior lines of endocrine therapy in the recurrent or metastatic setting to be eligible for the trial. Puma plans to initiate this trial in the second half of 2024.

Patients will be dosed with alisertib given at either 30 mg, 40 mg or 50 mg twice daily on days 1-3, 8-10 and 15-17 on a 28-day cycle in combination with the endocrine therapy of the investigator’s choice. Patients must not have been previously treated with the endocrine treatment that will be given in combination with alisertib in the trial. Each dose level will enroll up to 50 patients. Patients must provide blood samples and tissue-based biopsies so that biomarkers can be evaluated. The primary efficacy end points will include objective response rate, duration of response, disease control rate and progression-free survival. As a secondary endpoint, the Company will be evaluating each of these efficacy endpoints within biomarker subgroups in order to determine whether any biomarker subgroup correlates with response. The goal would be to enhance the efficacy in a biomarker subgroup to improve the efficacy of alisertib as previously seen in preclinical and clinical studies in other cancers, including breast cancer and small cell lung cancer.

Once the optimal alisertib dose is identified, the Company plans to engage with global regulatory agencies regarding the design of a pivotal (Phase III) trial, which it anticipates will be a randomized trial of alisertib plus investigators choice endocrine therapy versus placebo plus investigator’s choice endocrine therapy in patients with chemotherapy naïve HER2-negative, hormone receptor-positive metastatic breast cancer.

“Although there have been new drugs approved for the treatment of ER-positive HER2-negative metastatic breast cancer, there continues to be a need for new drugs and ones that specifically can address patients who have been previously treated with CDK 4/6 inhibitors,” said Alvin Wong, Pharm.D., Chief Scientific Officer of Puma Biotechnology. “The TBCRC 041 trial, which was published in JAMA Oncology in March 2023, demonstrated that alisertib is among the first investigational targeted therapies to have demonstrated encouraging clinical activity and have been generally well tolerated in the setting of endocrine and CDK 4/6 inhibitor resistant metastatic breast cancer. We look forward to the initiation of the ALISCA-Breast1 trial in the second half of 2024.”

Alan H. Auerbach, Chief Executive Officer and President of Puma Biotechnology, said, “We are excited to move forward with the development of alisertib in HER2-negative hormone receptor-positive metastatic breast cancer. We believe that the data from TBCRC 041, which tested alisertib alone and with fulvestrant, and the randomized trial of alisertib plus paclitaxel versus paclitaxel alone have demonstrated that alisertib was active in patients with HER2-negative, hormone receptor-positive metastatic breast cancer and in biomarker focused subgroups. We also recognize our fiscal responsibility to the shareholders of the Company and will be carefully managing the development expenses for alisertib so as not to potentially negatively impact the Company’s profitability.”

About Puma Biotechnology

Puma Biotechnology, Inc. is a biopharmaceutical company with a focus on the development and commercialization of innovative products to enhance cancer care. Puma in-licensed the global development and commercialization rights to PB272 (neratinib, oral), PB272 (neratinib, intravenous) and PB357. Neratinib, oral was approved by the U.S. Food and Drug Administration in 2017 for the extended adjuvant treatment of adult patients with early stage HER2-overexpressed/amplified breast cancer, following adjuvant trastuzumab-based therapy, and is marketed in the United States as NERLYNX® (neratinib) tablets. In February 2020, NERLYNX was also approved by the FDA in combination with capecitabine for the treatment of adult patients with advanced or metastatic HER2-positive breast cancer who have received two or more prior anti-HER2-based regimens in the metastatic setting. NERLYNX was granted marketing authorization by the European Commission in 2018 for the extended adjuvant treatment of adult patients with early stage hormone receptor-positive HER2-overexpressed/amplified breast cancer and who are less than one year from completion of prior adjuvant trastuzumab-based therapy. NERLYNX is a registered trademark of Puma Biotechnology, Inc.

In September 2022, Puma entered into an exclusive license agreement for the development and commercialization of the anti-cancer drug alisertib, an investigational, selective, small molecule, orally administered inhibitor of aurora kinase A. Initially, Puma intends to focus the development of alisertib on the treatment of small cell lung cancer and breast cancer. In February 2024, Puma initiated ALISCA-Lung 1, a Phase II clinical trial of alisertib monotherapy for the treatment of patients with extensive-stage small cell lung cancer.

Further information about Puma Biotechnology may be found at https://www.pumabiotechnology.com.

Forward-Looking Statements

This press release contains forward-looking statements, including statements regarding Puma’s anticipated milestones and the development of alisertib. All forward-looking statements involve risks and uncertainties that could cause Puma’s actual results to differ materially from the anticipated results and expectations expressed in these forward-looking statements. These statements are based on current expectations, forecasts and assumptions, and actual outcomes and results could differ materially from these statements due to a number of factors, which include, but are not limited to, the risk factors disclosed in the periodic and current reports filed by Puma with the Securities and Exchange Commission from time to time, including Puma’s Annual Report on Form 10-K for the year ended December 31, 2023 and subsequent reports. Readers are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date hereof. Puma assumes no obligation to update these forward-looking statements, except as required by law.

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