Seattle Genetics and Astellas Announce Positive Topline Results from Pivotal Trial of Enfortumab Vedotin in Locally Advanced or Metastatic Urothelial Cancer

– Companies Plan to Submit Biologics License Application Later This
Year –

– Seattle Genetics to Hold Conference Call Today at 9:00 a.m. EDT –

BOTHELL, Wash. & TOKYO–(BUSINESS WIRE)–Seattle
Genetics, Inc. (Nasdaq:SGEN) and Astellas
Pharma Inc. (TSE: 4503, President and CEO: Kenji Yasukawa, Ph.D.,
“Astellas”) today announced positive topline results from the first
cohort of patients in a pivotal phase 2 single-arm clinical trial known
as EV-201. The cohort is evaluating enfortumab vedotin for the treatment
of patients with locally advanced or metastatic urothelial cancer who
have received previous treatment with both platinum-containing
chemotherapy and a PD-1 or PD-L1 inhibitor. Results showed a 44 percent
objective response rate (ORR) per blinded independent central review.
The duration of response was consistent with that recently reported in
the previous phase 1 study (EV-101). The most common
treatment-related adverse events included fatigue, alopecia, decreased
appetite, rash and peripheral neuropathy. The data will be presented at
an upcoming medical meeting.

Enfortumab vedotin is an investigational antibody-drug conjugate (ADC)
that targets Nectin-4, a therapeutic target that is highly expressed in
multiple solid tumors including urothelial cancers. Based on preliminary
results from a phase 1 trial (EV-101), enfortumab vedotin was granted
Breakthrough Therapy designation by the U.S. Food and Drug
Administration (FDA) for patients with locally advanced or metastatic
urothelial cancer whose disease has progressed during or following
treatment with a PD-1 or PD-L1 inhibitor.

The companies plan to submit a Biologics License Application (BLA) to
the FDA later this year based on the results from the EV-201 trial
(cohort 1). A global, randomized phase 3 clinical trial (EV-301) is
ongoing and intended to support global registration as well as to serve
as the confirmatory randomized trial for enfortumab vedotin for patients
with locally advanced or metastatic urothelial cancer who have been
previously treated with a platinum-containing chemotherapy and a PD-1 or
PD-L1 inhibitor.

“Despite recent approvals of multiple checkpoint inhibitors for
previously treated locally advanced or metastatic urothelial cancer,
there remains a high unmet need for effective treatments upon
progression after initial chemotherapy and immunotherapy,” said Roger
Dansey, M.D., Chief Medical Officer at Seattle Genetics. “These results
for enfortumab vedotin indicate it may be able to help patients whose
urothelial cancer progresses following treatment with standard
chemotherapy and a PD-1 or PD-L1 inhibitor.”

“After progression on platinum-containing chemotherapy and a PD-1 or
PD-L1 inhibitor, patients with locally advanced or metastatic urothelial
cancer are left with no approved standard of care treatment options,”
said Steven Benner, M.D., Senior Vice President and Global Therapeutic
Area Head, Oncology Development at Astellas. “These data are very
encouraging, and we look forward to discussing the data with relevant
health authorities.”

Urothelial cancer is the most common type of bladder cancer (90 percent
of cases).¹ In 2018, more than 82,000 people were diagnosed
with bladder cancer in the United States.² Globally,
approximately 549,000 people were diagnosed with bladder cancer last
year, and there were approximately 200,000 deaths worldwide.³
Approximately 80 percent of people do not respond to PD-1 or PD-L1
inhibitors after a platinum-containing therapy has failed as an initial
treatment for advanced disease.⁴ There are currently no
approved therapies for metastatic urothelial cancer once it has
progressed after chemotherapy and a PD-1 or PD-L1 inhibitor.⁵

In addition to the ongoing confirmatory phase 3 study intended to also
support global registration, development of enfortumab vedotin is
underway in earlier lines of treatment for locally advanced or
metastatic urothelial cancer, including in newly diagnosed patients in
combination with pembrolizumab and/or platinum chemotherapy.

About The EV-201 Trial

EV-201 is an ongoing single-arm, pivotal phase 2 clinical trial of
enfortumab vedotin for patients with locally advanced or metastatic
urothelial cancer who have been previously treated with a PD-1 or PD-L1
inhibitor, including those who have also been treated with a
platinum-containing chemotherapy (cohort 1) and those who have not
received a platinum-containing chemotherapy and who are ineligible for
cisplatin (cohort 2). The EV-201 phase 2 trial continues to enroll
patients in cohort 2. In cohort 1, 128 patients were enrolled at
multiple centers internationally.⁶ The primary endpoint is
confirmed objective response rate per blinded independent central
review. Secondary endpoints include assessments of duration of response,
disease control rate, progression-free survival, overall survival,
safety and tolerability. More information about enfortumab vedotin
clinical trials can be found at clinical
trials.gov.

About Enfortumab Vedotin

Enfortumab vedotin is an investigational ADC composed of an
anti-Nectin-4 monoclonal antibody attached to a microtubule-disrupting
agent (MMAE) using Seattle Genetics’ proprietary linker technology.
Enfortumab vedotin targets Nectin-4, a cell adhesion molecule identified
as an ADC target by Astellas, which is expressed on many solid tumors.

The safety and efficacy of enfortumab vedotin are under investigation
and have not been established. There is no guarantee that the agent will
receive regulatory approval and become commercially available for the
uses being investigated.

Seattle Genetics Conference Call Details

Seattle Genetics’ management will host a conference call and webcast to
discuss the announcement of enfortumab vedotin topline data. The event
will be held today at 6:00 a.m. Pacific Time (PT); 9:00 a.m. Eastern
Time (ET). The live event will be available from the Seattle Genetics
website at www.seattlegenetics.com,
under the Investors section, or by calling 866-288-0540 (domestic) or
786-460-7199 (international). The conference ID is 3807860. A replay of
the live event will be available starting on March 28, 2019 on the
Seattle Genetics website or by calling 888-203-1112 (domestic) or
719-457-0820 (international), using conference ID 3807860. The telephone
replay will be available until 5:00 p.m. PT on April 1, 2019.

About Seattle Genetics

Seattle Genetics, Inc. is an emerging multi-product, global
biotechnology company that develops and commercializes transformative
therapies targeting cancer to make a meaningful difference in people’s
lives. The company is headquartered in Bothell, Washington, and has a
European office in Switzerland. For more information on our robust
pipeline, visit www.seattlegenetics.com
and follow @SeattleGenetics on Twitter.

About Astellas

Astellas Pharma Inc., based in Tokyo, Japan, is a company dedicated to
improving the health of people around the world through the provision of
innovative and reliable pharmaceutical products. For more information,
please visit our website at https://www.astellas.com/en.

About the Astellas and Seattle Genetics Collaboration

Seattle Genetics and Astellas are co-developing enfortumab vedotin under
a collaboration that was entered into in 2007, and expanded in 2009.
Under the collaboration, the companies are sharing costs and profits on
a 50:50 basis worldwide.

Seattle Genetics Forward Looking Statement

Certain statements made in this press release are forward looking, such
as those, among others, relating to the companies’ expected reporting of
data from cohort 1 of the EV-201 trial in upcoming medical conferences,
and plan to submit a Biologics License Application (BLA) to the FDA in
the near term under FDA’s Accelerated Approval program based on the
results of the pivotal EV-201 trial; conduct of a comprehensive clinical
development program for enfortumab vedotin, which includes an ongoing
randomized phase 3 confirmatory trial (EV-301) intended to support
global registration in locally advanced or metastatic urothelial cancer;
and the therapeutic potential of enfortumab vedotin, its possible
safety, efficacy, and therapeutic uses; and anticipated development
activities including future clinical trials and intended regulatory
actions. Actual results or developments may differ materially from those
projected or implied in these forward-looking statements. Factors that
may cause such a difference include that the data from EV-201 may not be
selected for publication at medical conferences; the possibility of
delays in the submission of a BLA to the FDA; that the data from EV-201
may not be sufficient to support accelerated approval; and the inability
to show sufficient activity in EV-301 and subsequent clinical trials;
the risk of adverse events or safety signals; and the possibility of
adverse regulatory actions as enfortumab vedotin advances in clinical
trials even after promising results in earlier clinical trials. More
information about the risks and uncertainties faced by Seattle Genetics
is contained under the caption “Risk Factors” included in the company’s
Annual Report on Form 10-K for the year ended December 31, 2018 filed
with the Securities and Exchange Commission. Seattle Genetics disclaims
any intention or obligation to update or revise any forward-looking
statements, whether as a result of new information, future events or
otherwise.

Astellas Cautionary Notes

In this press release, statements made with respect to current plans,
estimates, strategies and beliefs and other statements that are not
historical facts are forward-looking statements about the future
performance of Astellas. These statements are based on management’s
current assumptions and beliefs in light of the information currently
available to it and involve known and unknown risks and uncertainties. A
number of factors could cause actual results to differ materially from
those discussed in the forward-looking statements. Such factors include,
but are not limited to: (i) changes in general economic conditions and
in laws and regulations, relating to pharmaceutical markets, (ii)
currency exchange rate fluctuations, (iii) delays in new product
launches, (iv) the inability of Astellas to market existing and new
products effectively, (v) the inability of Astellas to continue to
effectively research and develop products accepted by customers in
highly competitive markets, and (vi) infringements of Astellas’
intellectual property rights by third parties.

Information about pharmaceutical products (including products currently
in development), which is included in this press release is not intended
to constitute an advertisement or medical advice.

¹ American Society of Clinical Oncology. Bladder Cancer:
Introduction (10-2017). https://www.cancer.net/cancer-types/bladder-cancer/introduction.

² https://gco.iarc.fr/today/data/factsheets/populations/840-united-states-of-america-fact-sheets.pdf

³ Bray F, Ferlay J, Soerjomataram I, Siegel RL, Torre LA,
Jemal A. Global cancer statistics 2018: GLOBOCAN estimates of incidence
and mortality worldwide for 36 cancers in 185 countries. CA Cancer J
Clin. 2018;68(6):394-424.

⁴ Alhalabi O, Shah AY, Lemke EA, Gao J (2019). Immune
checkpoint inhibitors in urothelial cancer. Oncology (Williston Park)
33(1): 1108.

⁵ National Comprehensive Cancer Network. Bladder Cancer
(Version 1.2019). http://www.nccn.org/professionals/physician_gls/pdf/bladder.pdf.

⁶ Data on file at Seattle Genetics

Contacts

Seattle Genetics:
For Media
Monique Greer
Vice
President, Corporate Communications
(425) 527-4641
[email protected]

For Investors
Peggy Pinkston
Vice President, Investor
Relations
(425) 527-4160
[email protected]

Astellas:
For Media
Marjorie Moeling
Director,
Corporate Affairs
(224) 205-5205
[email protected]

For Investors
Shin Okubo
Executive Director, Investor
Relations
+81-3-3244-3202
[email protected]