Puma Biotechnology Presents 3-Year Disease Free Survival Data from Phase III Trial of PB272 in Extended Adjuvant Breast Cancer (ExteNET Trial) at the 2015 San Antonio Breast Cancer Symposium

LOS ANGELES–(BUSINESS WIRE)–Puma Biotechnology, Inc. (NYSE: PBYI), a biopharmaceutical company,
announced the presentation of updated results from the Phase III
clinical trial of Puma’s investigational drug PB272 (neratinib) for the
extended adjuvant treatment of breast cancer (ExteNET trial). 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. The
data was presented today in an oral presentation at the 2015 CTRC-AACR
San Antonio Breast Cancer Symposium (SABCS) that is currently taking
place in San Antonio, Texas. Previous safety and efficacy data from this
trial were reported in June at the American Society of Clinical Oncology
(ASCO) 2015 Annual Meeting in Chicago, Illinois.

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 DFS rate for the neratinib arm was
93.9% and the 2-year DFS rate for the placebo arm was 91.6%. These
results were previously reported at the 2015 American Society of
Clinical Oncology meeting in June.

The presentation at SABCS involved an exploratory sensitivity analysis
of the 3-year disease free survival data to examine the durability of
treatment effect beyond the 2-year data included in the primary
analysis. This analysis was not a pre-planned analysis in the
statistical analysis plan for the trial. For the primary endpoint of the
trial, invasive disease free survival (DFS), the 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, two sided p = 0.023). The 3-year DFS rate for the
neratinib arm was 92.0% and the 3-year DFS rate for the placebo arm was
89.9%.

The previously published analysis of previous adjuvant trials of
Herceptin have demonstrated that patients are at the highest risk of
disease progression closest to the completion of their treatment with
adjuvant trastuzumab (Perez et al, Journal of Clinical Oncology, 2014).
For the 2,297 patients in the ExteNET trial who were treated in ExteNET
less than one year from the completion of their adjuvant treatment with
trastuzumab, the results of the trial demonstrated that treatment with
neratinib resulted in a 28% reduction of risk of invasive disease
recurrence or death versus placebo (hazard ratio = 0.72, two sided p =
0.02). For this group of patients, the 3-year DFS rate for the neratinib
arm was 91.5% and the 3-year DFS rate for the placebo arm was 88.9%.

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 2,041 (72%) of the patients in the ExteNET trial, and
further central testing on available samples is currently ongoing. For
the 1,709 patients whose tumors were HER2 positive by central
confirmation, the 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, two sided p =
0.037). The 3-year DFS rate for the centrally confirmed patients in the
neratinib arm was 91.8% and the 3-year DFS rate for the centrally
confirmed patients in the placebo arm was 89.6%. For the 1,392 patients
in the ExteNET trial with centrally confirmed HER2 positive disease who
were treated in ExteNET less than one year from the completion of their
adjuvant treatment with trastuzumab, the results of the trial
demonstrated that treatment with neratinib resulted in a 37% reduction
of risk of invasive disease recurrence or death versus placebo (hazard
ratio = 0.63, two sided p = 0.009). For this group of patients, the
3-year DFS rate for the neratinib arm was 91.7% and the 3-year DFS rate
for the placebo arm was 88.2%.

For the pre-defined subgroup of 1,631 patients with hormone receptor
positive disease, the results of the trial demonstrated that treatment
with neratinib resulted in a 43% reduction of risk of invasive disease
recurrence or death versus placebo (hazard ratio = 0.57, two sided p =
0.003). The 3-year DFS rate for the neratinib arm was 93.6% and the
3-year DFS rate for the placebo arm was 89.3%. For the 1,334 hormone
receptor positive patients in the ExteNET trial who were treated in
ExteNET less than one year from the completion of their adjuvant
treatment with trastuzumab, the results of the trial demonstrated that
treatment with neratinib resulted in a 43% reduction of risk of invasive
disease recurrence or death versus placebo (hazard ratio = 0.57, two
sided p = 0.004). For this group of patients, the 3-year DFS rate for
the neratinib arm was 93.3% and the 3-year DFS rate for the placebo arm
was 88.6%. For the 903 patients in the trial whose tumors were hormone
receptor positive and HER2 positive by central confirmation, the results
of the trial demonstrated that treatment with neratinib resulted in a
57% reduction of risk of invasive disease recurrence or death versus
placebo (hazard ratio = 0.43, two sided p < 0.001). The 3-year DFS rate
for the hormone receptor positive patients who also had HER2 centrally
confirmed disease in the neratinib arm was 94.4% and the 3-year DFS rate
for centrally confirmed patients in the placebo arm was 88.0%.

“While the use of adjuvant trastuzumab has led to a reduction in disease
recurrence in patients with early stage HER2-positive breast cancer,
there remains an unmet clinical need to further reduce this risk of
recurrence,” said Professor Arlene Chan, medical oncologist at Mount
Hospital and the Vice Chair of the Breast Cancer Research Centre WA.
“This exploratory analysis shows that the results of the ExteNET study
demonstrate that we may be able to provide this type of improvement with
neratinib to further help the patients with this disease and that the
treatment effect of neratinib appears to be maintained over time.”

“We are very pleased with these 3-year DFS follow up results from the
ExteNET trial with neratinib. We continue to be pleased with the
activity of neratinib in this group of patients and more specifically
with the centrally confirmed HER2 cohorts and the hormone receptor
positive subgroup of patients,” said Alan H. Auerbach, Chief Executive
Officer and President of Puma. “We look forward to proceeding with the
regulatory filings for neratinib for the extended adjuvant treatment of
breast cancer in the United States and Europe, currently anticipated in
the first quarter and first half of 2016, respectively.”

Conference Call and Webcast

The Company will host a conference call to discuss its ExteNET trial
data presented at the SABCS at 12:00 p.m. CST (10:00 a.m. PST, 1:00 p.m.
EST) on Friday, December 11, 2015. The conference call may be accessed
by dialing 1-877-709-8150 for domestic callers and 1-201-689-8354 for
international callers. Please specify to the operator that you would
like to join the “Puma Biotechnology Update Call.” The conference call
will be webcast live and accessible through the Investor Relations
section of Puma’s website at http://www.pumabiotechnology.com/ir_events.html
and will be archived there for 30 days following the call. Please visit
Puma’s website several minutes prior to the start of the broadcast to
ensure adequate time for any software download that may be necessary.

About Puma Biotechnology

Puma Biotechnology, Inc. is a biopharmaceutical company with a focus on
the acquisition, development and commercialization of innovative
products to enhance cancer care. The Company aims to acquire proprietary
rights to these products, by license or otherwise, fund their research
and development and bring the products to market. The Company is
initially focused on the development of PB272 (oral neratinib), a potent
irreversible tyrosine kinase inhibitor, for the treatment of patients
with HER2-positive breast cancer and patients with non-small cell lung
cancer, breast cancer and other solid tumors that have a HER2 mutation.

Further information about Puma Biotechnology can be found at www.pumabiotechnology.com.

Forward-Looking Statements:

This press release contains forward-looking statements, including, but
not limited to, statements regarding the development of our drug
candidates and the timing of regulatory filings. 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 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, 2014 and any subsequently filed Quarterly
Reports on Form 10-Q and Current Reports on Form 8-K. 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
Robert E. Flamm, Ph.D. or David Schull, +1 212-845-4226
robert.flamm@russopartnersllc.com
david.schull@russopartnersllc.com