Puma Biotechnology Presents Interim Results of Phase II Trial of PB272 for ERBB2 Mutant, HER2 Non-Amplified, Metastatic Breast Cancer at the 2015 San Antonio Breast Cancer Symposium

LOS ANGELES–(BUSINESS WIRE)–Puma Biotechnology, Inc. (NYSE: PBYI), a biopharmaceutical company,
announced that interim results from an ongoing Phase II clinical trial
of Puma’s investigational drug PB272 (neratinib) were presented at the
2015 CTRC-AACR San Antonio Breast Cancer Symposium (SABCS) that is
currently taking place in San Antonio, Texas. The presentation entitled
“Neratinib for ERBB2 mutant, HER2 non-amplified, metastatic breast
cancer: preliminary analysis from SUMMIT – a multicenter, open-label,
multi-histology phase II basket trial” will be presented as a poster
discussion by Dr. David Hyman, Acting Director, Developmental
Therapeutics at Memorial Sloan Kettering Cancer Center.

In May 2014 Puma announced that it expanded the first cohort from the
Phase II clinical trial of PB272 (neratinib) in patients with solid
tumors who have an activating ERBB2 (HER2) mutation (SUMMIT
basket trial). These interim results are the first presentation of data
from this expanded cohort of patients with metastatic breast cancer and
whose tumors have a HER2 mutation but are neither HER2 amplified or
overexpressed (HER2 negative).

In the cohort, patients with HER2 mutant metastatic breast cancer were
enrolled and 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 20 patients in the cohort presented, 20 patients (100%) had
HER2-negative disease, 17 patients (85%) were hormone receptor positive
(estrogen receptor or progesterone receptor positive), and patients had
received a median of 4 prior regimens in the metastatic setting (range
0-11 prior regimens) before entering the trial.

The primary endpoint of the trial was objective response at week 8
assessed by anatomic or metabolic imaging. The interim efficacy results
from the trial showed that for the 19 efficacy evaluable patients in the
breast cancer cohort, 6 patients (32%) experienced a response at week 8.
This included one patient with a complete response and five patients
with partial responses. The secondary endpoints of the trial included
confirmed objective response (complete response or partial response),
clinical benefit rate and progression free survival (PFS). The results
of the trial showed that 3 patients (16%) had a confirmed objective
response, 8 patients (42%) demonstrated clinical benefit and the median
progression free survival was 4.0 months.

The presentation also discussed that a bidirectional cross-talk between
hormone receptor and HER2 signaling pathways can lead to endocrine
resistance due to activated HER2 signaling and ER-mediated tumor
proliferation as a potential resistance mechanism to sustained HER2
inhibition. Preclinical data 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-positive breast tumors. Based on this, the SUMMIT study
was amended to allow for the combination of neratinib plus fulvestrant
in eligible postmenopausal hormone receptor positive breast cancer
patients. For the 3 response-evaluable patients who have been enrolled
and received the combination of neratinib plus fulvestrant, 3 (100%) of
3 patients have shown a response, including one patient with a complete
response and two patients with partial responses. There have also been
two patients enrolled on the combination of neratinib plus fulvestrant
after progressing on neratinib monotherapy. One (50%) of these two
patients has demonstrated a partial response.

The interim safety results of the study showed that the most frequently
observed adverse event was diarrhea. For the 130 patients enrolled
across all solid tumor cohorts in the SUMMIT study, 25 patients (19%)
reported grade 3 diarrhea. The median duration of grade 3 diarrhea for
the patients in the entire SUMMIT study was 2 days. 2 patients (2%) in
the SUMMIT study have permanently discontinued neratinib due to diarrhea
and 20 patients (15%) have temporarily discontinued neratinib due to
diarrhea and then restarted after the diarrhea subsided. For the breast
cancer mutation cohort, 7 of 20 patients (35%) experienced grade 3
diarrhea. The median duration of grade 3 diarrhea was 1 day. No patient
(0%) in the breast cancer cohort permanently discontinued neratinib due
to diarrhea and 4 patients (20%) temporarily discontinued neratinib due
to diarrhea and then restarted after the diarrhea subsided.

Dr. David Hyman, Acting Director, Developmental Therapeutics at Memorial
Sloan Kettering Cancer Center and principal investigator of the trial,
stated, “Neratinib showed promising signs of clinical activity as a
single agent and very encouraging clinical activity in the patients with
the combination of neratinib plus fulvestrant in this interim analysis
of pre-treated HER2 mutant breast cancer patients. The safety profile of
the drug was manageable and the diarrhea was not treatment-limiting with
appropriate prophylaxis and management. We look forward to completing
the ongoing neratinib plus fulvestrant cohort and initiating the pivotal
trial of the combination that we are currently planning for 2016.”

Alan H. Auerbach, Chief Executive Officer and President of Puma
Biotechnology, said, “We are very pleased with the preliminary activity
seen with neratinib, both alone and in combination with fulvestrant in
this cohort of patients with HER2 mutated breast cancer. We look forward
to the completion of the trial and advancing the combination of PB272
and fulvestrant into a pivotal trial in 2016.”

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 anticipated timing for the commencement and
completion of various clinical 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 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.


Puma Biotechnology, Inc.
Alan H. Auerbach or Mariann Ohanesian, +1
424 248 6500
Robert E. Flamm, Ph.D. or David Schull, +1 212 845 4226