Puma Biotechnology Presents Positive Phase II Data at the 2016 ASCO Annual Meeting

LOS ANGELES–(BUSINESS WIRE)–Puma Biotechnology, Inc. (NYSE: PBYI), a biopharmaceutical company,
presented positive results from an investigator-sponsored Phase II trial
of neratinib with HER2-mutated, non-amplified breast cancer. The data
were presented today in a poster discussion session at the American
Society of Clinical Oncology (ASCO) 2016 Annual Meeting in Chicago,
Illinois. The poster (Abstract #516), entitled “Phase II Trial of
Neratinib for HER2 Mutated, Non-Amplified Metastatic Breast Cancer (HER2^mutMBC),”
was presented from 8:00-11:30 a.m. CDT today with a poster presentation
discussion occurring immediately following the poster session.

In the trial, patients with HER2 mutated breast cancer (either in their
primary or metastatic tumor) received 240 mg of neratinib daily.
Patients received loperamide (16 mg per day initially) prophylactically
for the first cycle of treatment in order to reduce the
neratinib-related diarrhea. For the 16 patients enrolled in the trial,
16 patients (100%) had HER2-negative disease, 15 patients (94%) were
hormone receptor positive (estrogen receptor or progesterone receptor
positive), and for the patients with metastatic disease, patients had
received a median of 3 prior regimens (range 2-10 prior regimens) before
entering the trial. Among these 16 patients, 14 had activating HER2
mutations and 2 patients had HER2 mutations of unknown
significance.

The primary endpoint of the Phase II trial was clinical benefit rate
(CBR), defined as complete response (CR), partial response (PR) or
stable disease (SD) greater than or equal to 6 months. The trial was
designed to detect a CBR of 20%. In the 14 patients with activating HER2
mutations, 5/14 (36%) achieved clinical benefit, including 1 patient
(7%) with a CR, 1 patient (7%) with a PR, and 3 patients (21%) with SD
for greater than or equal to 6 months. The median duration of response
in these 5 patients was 6 (range 6-14+) months. The median
progression-free survival for all 14 patients with activating HER2
mutations in the trial was 5.0 months. In the 2 patients with HER2 mutations
of unknown significance, there was no clinical benefit seen with
neratinib.

Based on the preclinical data that has demonstrated that the combination
of an anti-estrogen with a HER2 inhibitor results in enhanced anti-tumor
activity in preclinical models of estrogen receptor
positive/HER2-mutated breast tumors, the study has been amended to
administer the combination of neratinib plus fulvestrant in eligible
hormone receptor positive breast cancer patients who have an activating
HER2 mutation in the tumor. Enrollment in this cohort is currently
ongoing and results from this cohort receiving the combination of
fulvestrant plus neratinib will be presented at a future medical meeting.

The interim safety results of the study showed that the most frequently
observed adverse event was diarrhea. For the 16 patients enrolled in the
study, 4 patients (25%) reported grade 3 diarrhea. The median duration
of grade 3 diarrhea for the patients in the study was 1.5 days.

Dr. Cynthia Ma, Associate Professor of Medicine, Clinical Director of
the Breast Cancer Program, Section of Medical Oncology, Division of
Oncology, at Washington University School of Medicine and principal
investigator of the trial, stated, “Neratinib showed promising clinical
activity as a single agent in this trial in patients with HER2,
non-amplified breast cancer that has an activating HER2 mutation. We
look forward to continuing to enroll the cohort that is receiving the
combination of neratinib plus fulvestrant and to reporting those results
at a future medical meeting.”

Alan H. Auerbach, Chief Executive Officer and President of Puma
Biotechnology, said, “We are very pleased with the preliminary activity
seen with neratinib in this cohort of patients with HER2-mutated breast
cancer. We look forward to advancing the clinical development of the
combination of neratinib and fulvestrant and determining the potential
registration path for this combination in 2016.”

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 anticipated timing relating to clinical trials
and the announcement of data relative to these trials. 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
Robert Flamm or David Schull
+1-212-845-4235
robert.flamm@russopartnersllc.com
david.schull@russopartnersllc.com