On December 7, 2016 Puma Biotechnology, Inc. (NYSE: PBYI), a biopharmaceutical company, reported that a biomarker analysis of the NSABP FB-7 Phase II clinical trial of Puma’s investigational drug PB272 (neratinib) was presented at the 2016 CTRC-AACR San Antonio Breast Cancer Symposium (SABCS) that is currently taking place in San Antonio, Texas (Press release, Puma Biotechnology, DEC 7, 2016, View Source [SID1234516991]). The presentation entitled "An exploratory correlative biomarker analysis of NSABP FB-7, a phase II randomized trial evaluating neoadjuvant therapy with weekly paclitaxel (P) plus neratinib (N) or trastuzumab (T) or neratinib and trastuzumab (N+T) followed by doxorubicin and cyclophosphamide (AC) with postoperative T in women with locally advanced HER2-positive breast cancer" was presented as a poster presentation. This trial was sponsored by the NSABP Foundation, Inc.
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The FB-7 trial is a randomized Phase II clinical trial for women with HER2-positive locally advanced stage IIB-IIIC invasive breast cancer. Patients were randomly assigned to receive trastuzumab (T) or neratinib (N) or the combination (T+N) with weekly paclitaxel (P) followed by standard doxorubicin and cyclophosphamide chemotherapy (AC) administered prior to surgery. 126 U.S., Canadian, and European patients were randomly assigned to Arm 1 (T+P followed by AC), Arm 2 (N+P followed by AC) or Arm 3 (T+N+P followed by AC). The primary endpoint of the trial was pathological complete response rate (pCR) in the breast and lymph nodes. The clinical safety and efficacy data from this trial was presented at the 2015 SABCS.
A key secondary endpoint of the FB-7 trial was to evaluate molecular and genetic markers for correlation with response. Pre-treatment core biopsy samples (n=59) and post treatment surgical samples (n=17) were obtained from a subset of patients treated in the FB-7 trial. pCR data were available for 51 patients from the biomarker cohort. After excluding low tumor content non-evaluable samples, correlative biomarker analysis was performed in 42 patients.
Expression levels and the activation status of EGFR/HER2 signaling proteins were investigated. The results of the phosphorylated HER2 (phosphoHER2) showed that median levels of phosphoHER2 were higher in the patients who achieved a pCR with neratinib (n=7) than in the patients who did not achieve a pCR who received either trastuzumab (n=8, p=0.07) or the combination of trastuzumab plus neratinib (n=4, p=0.035). There was not a significant difference in the median levels of phosphoHER2 in the patients who achieved a pCR with neratinib (n=7), trastuzumab (n=8, p=0.16) or the combination of trastuzumab plus neratinib (n=4, p=0.10).
The truncated form of HER2 known as p95HER2 was measured by the proprietary assay of Pierian Bioscience. p95HER2 represents a truncated form of the HER2 receptor that lacks the extracellular trastuzumab binding domain. It is believed to represent a mechanism of trastuzumab resistance. Median p95HER2 levels were higher in samples from patients who achieved a pCR with neratinib than in the patients who did not achieve a pCR who received either trastuzumab (p=0.027) or the combination of trastuzumab plus neratinib (p=0.009). There was not a significant difference in the median levels of p95HER2 in the patients who achieved a pCR with neratinib (n=7), trastuzumab (n=8, p=0.16) or the combination of trastuzumab plus neratinib (n=4, p=0.35).
The MammaPrint assay was performed on 59 samples to determine if there was any imbalance between arms. This assay is a genomic test that analyzes the activity of 70 genes and then calculates a recurrence score that is either low risk or high risk. The results of the MammaPrint showed that the patients in all three arms of the FB-7 trial were balanced with the median MammaPrint risk score being similar across arms. There were only three patients with a MammaPrint low score.
Dr. Samuel Jacobs, Emeritus Clinical Professor in the Department of Medicine, University of Pittsburgh School of Medicine, and the Director of Medical Affairs for the NSABP Foundation, Inc., said, "We are pleased to see the results of this exploratory biomarker analysis which suggests that activation of the HER pathway based on p95HER2 and phosphoHER2 may correlate with pCR to neratinib. Further biomarker analysis in additional datasets will be needed to determine which patients may derive the greatest benefit from neratinib."
Alan H. Auerbach, Chief Executive Officer and President of Puma Biotechnology, said, "We are pleased to complete this biomarker analysis of neratinib. Further results of the biomarker analysis should help us to determine the best path forward for neratinib in the neoadjuvant treatment of HER2-positive early stage breast cancer."