Puma Biotechnology Presents Results of Biomarker Analysis of Phase II Trial of PB272 in Neoadjuvant Treatment of HER2-Positive Locally Advanced Breast Cancer at the 2016 San Antonio Breast Cancer Symposium

LOS ANGELES–(BUSINESS WIRE)–Puma Biotechnology, Inc. (NYSE: PBYI), a biopharmaceutical company,
announced 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. 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.

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.”

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. The Company in-licenses the global development and
commercialization rights to three drug candidates—PB272 (neratinib
(oral)), PB272 (neratinib (intravenous)) and PB357. Neratinib is a
potent irreversible tyrosine kinase inhibitor that blocks signal
transduction through the epidermal growth factor receptors, HER1, HER2
and HER4. Currently, the Company is primarily focused on the development
of the oral version of neratinib, and its most advanced drug candidates
are directed at the treatment of HER2-positive breast cancer. The
Company believes that neratinib has clinical application in the
treatment of several other cancers as well, including non-small cell
lung cancer and other tumor types that over-express or have a mutation
in HER2. Further information about Puma Biotechnology can be found at www.pumabiotechnology.com.

Forward-Looking Statements:

This press release contains forward-looking statements, including
statements regarding the development of the Company’s drug candidates.
All forward-looking statements included in this press release involve
risks and uncertainties that could cause the Company’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 fact
that the Company has no product revenue and no products approved for
marketing, the Company’s dependence on PB272, which is still under
development and may never receive regulatory approval, the challenges
associated with conducting and enrolling clinical trials, the risk that
the results of clinical trials may not support the Company’s drug
candidate claims, even if approved, the risk that physicians and
patients may not accept or use the Company’s products, the Company’s
reliance on third parties to conduct its clinical trials and to
formulate and manufacture its drug candidates, the Company’s dependence
on licensed intellectual property, and the other risk factors disclosed
in the periodic and current reports filed by the Company with the
Securities and Exchange Commission from time to time, including the
Company’s Annual Report on Form 10-K for the year ended December 31,
2015. Readers are cautioned not to place undue reliance on these
forward-looking statements, which speak only as of the date hereof. The
Company assumes no obligation to update these forward-looking
statements, except as required by law.

Contacts

Puma Biotechnology, Inc.
Alan H. Auerbach or Mariann Ohanesian,
+1-424-248-6500
info@pumabiotechnology.com
ir@pumabiotechnology.com
or
Russo
Partners
David Schull or Darren Chia, +1-212-845-4271
david.schull@russopartnersllc.com
darren.chia@russopartnersllc.com