On July 21, 2016 Puma Biotechnology, Inc. (NYSE: PBYI), a biopharmaceutical company, reported updated results from the Phase III clinical trial of Puma’s investigational drug PB272 (neratinib) for the extended adjuvant treatment of HER2-positive early stage breast cancer (ExteNET trial) (Press release, Puma Biotechnology, JUL 21, 2016, View Source [SID:1234513986]). The ExteNET trial is a double-blind, placebo-controlled, Phase III trial of neratinib versus placebo after adjuvant treatment with trastuzumab (Herceptin) in women with early stage HER2-positive breast cancer. Schedule your 30 min Free 1stOncology Demo! The ExteNET trial randomized 2,840 patients in 41 countries with early-stage HER2-positive breast cancer who had undergone surgery and adjuvant treatment with trastuzumab. After completion of adjuvant treatment with trastuzumab, patients were randomized to receive extended adjuvant treatment with either neratinib or placebo for a period of one year. Patients were then followed for recurrent disease, ductal carcinoma in situ, or death for a period of two years after randomization in the trial. The primary endpoint of the trial was invasive disease free survival (DFS). The results of the trial demonstrated that treatment with neratinib resulted in a 33% reduction of risk of invasive disease recurrence or death versus placebo (hazard ratio = 0.67, p = 0.009). The 2-year invasive DFS rate for the neratinib arm was 93.9% and the 2-year invasive DFS rate for the placebo arm was 91.6%. These results were previously reported at the 2015 American Society of Clinical Oncology (ASCO) (Free ASCO Whitepaper) meeting and updated results, including interim 3-year invasive DFS data, were presented at the 2015 CTRC-AACR San Antonio Breast Cancer Symposium (SABCS).
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As part of the data analysis for the New Drug Application (NDA) filing in the United States and the Marketing Authorisation Application (MAA) submission in Europe, an updated analysis that included an interim 5-year invasive DFS analysis was performed. This data analysis was performed in order to examine the durability of treatment effect beyond the 2-year data included in the primary analysis. This interim analysis was not a pre-planned analysis in the statistical analysis plan for the trial. For the primary endpoint of the trial, invasive DFS, the 5-year interim results of the trial demonstrated that treatment with neratinib resulted in a 26% reduction of risk of invasive disease recurrence or death versus placebo (hazard ratio = 0.74, p = 0.017). The 5-year interim invasive DFS rate for the neratinib arm was 90.4% and the 5-year interim invasive DFS rate for the placebo arm was 87.9%. Additional updated results for the 3-year invasive DFS rate and 4-year invasive DFS rate are shown in the table below:
DFS for Intent to Treat (ITT) Population
3-Year DFS 4-Year DFS 5-Year Interim DFS
Neratinib 92.5% 91.4% 90.4%
Placebo 90.3% 89.2% 87.9%
Absolute invasive DFS
Difference 2.2% 2.2% 2.5%
As an inclusion criteria for the ExteNET trial, patients needed to have tumors that were HER2 positive using local assessment. In addition, as a pre-defined subgroup in the trial, patients had centralized HER2 testing performed on their tumor as well. To date, centralized HER2 testing has been performed on 2,140 (75%) of the patients in the ExteNET trial, and further central testing on available samples is currently ongoing. For the 1,777 patients whose tumors were HER2 positive by central confirmation, the interim results of the trial demonstrated that treatment with neratinib resulted in a 30% reduction of risk of invasive disease recurrence or death versus placebo (hazard ratio = 0.70, p = 0.026). The 5-year interim invasive DFS rate for the centrally confirmed patients in the neratinib arm was 90.8% and the 5-year interim invasive DFS rate for the centrally confirmed patients in the placebo arm was 88.1%.
For the pre-defined subgroup of 1,631 patients with hormone receptor positive disease, the interim results of the trial demonstrated that treatment with neratinib resulted in a 41% reduction of risk of invasive disease recurrence or death versus placebo (hazard ratio = 0.59, p = 0.002). The 5-year interim invasive DFS rate for the neratinib arm was 91.7% and the 5-year interim invasive DFS rate for the placebo arm was 86.9%. Additional updated results for the 3-year invasive DFS rate and 4-year invasive DFS rate are shown in the table below:
DFS for Hormone Receptor Positive (HR-positive) Population
3-Year DFS 4-Year DFS 5-Year Interim DFS
Neratinib 93.8% 92.9% 91.7%
Placebo 89.9% 88.6% 86.9%
Absolute invasive DFS
Difference 3.9% 4.3% 4.8%
"We are very pleased with the interim 5-year invasive DFS results from the ExteNET trial with neratinib," said Alan H. Auerbach, Chief Executive Officer and President of Puma. "We believe these results support the long term clinical benefit of neratinib in the extended adjuvant treatment of patients with early stage HER2-positive breast cancer who have completed prior trastuzumab-based adjuvant therapy. We look forward to obtaining the full 5-year DFS data, which we anticipate will be available in 2017."