Seattle Genetics Announces Global License Agreement with Immunomedics for Sacituzumab Govitecan (IMMU-132), a Promising Late-Stage ADC for Solid Tumors

-Seattle Genetics to Lead Development, Manufacturing and
Commercialization of Sacituzumab Govitecan Globally-

-Planned BLA for Triple Negative Breast Cancer Indication; Other
Solid Tumors Being Explored in the Clinic-

-Conference Call Today at 8:30 a.m. ET-

BOTHELL, Wash.–(BUSINESS WIRE)–Seattle
Genetics, Inc. (Nasdaq: SGEN), a global biotechnology company, today
announced a development and license agreement with Immunomedics,
Inc. (Nasdaq: IMMU) under which Seattle Genetics would receive
exclusive worldwide rights to develop, manufacture and commercialize
sacituzumab govitecan (IMMU-132). Sacituzumab govitecan is an
antibody-drug conjugate (ADC) targeted to TROP-2, which is expressed in
several solid tumors including cancers of the breast, lung and bladder.
Sacituzumab govitecan is in a phase 1/2 trial for patients with triple
negative breast cancer (TNBC), as well as multiple other solid tumors.
It received Breakthrough Therapy Designation from the U.S. Food and Drug
Administration (FDA) for the treatment of patients with TNBC who have
failed prior therapies for metastatic disease. Data from the phase 1/2
trial are intended to serve as the basis for a planned Biologics License
Application (BLA) submission under the FDA’s accelerated approval
regulations.

“This agreement would add a promising late-stage ADC to our pipeline as
we continue making progress towards our goal of becoming a global,
multi-product oncology company. Sacituzumab govitecan would complement
our existing pipeline by providing a potential near-term opportunity to
commercialize a second drug in the United States, expand our
international capabilities in Europe and elsewhere and extend our
efforts in solid tumors,” said Clay Siegall, Ph.D., President and Chief
Executive Officer of Seattle Genetics. “In addition, we believe our
expertise in ADCs, including demonstrated success in clinical
development, regulatory, manufacturing and commercialization, ideally
positions Seattle Genetics to advance this program globally. We look
forward to working with Immunomedics to advance this program for
patients in need, including those with triple negative breast cancer and
other solid tumors.”

Cynthia L. Sullivan, President and Chief Executive Officer of
Immunomedics, said, “After a long and robust process, we concluded that
licensing our lead asset, sacituzumab govitecan, to Seattle Genetics,
the leading ADC company, would give us the best opportunity to advance
this product on behalf of advanced stage cancer patients. Sacituzumab
govitecan has the potential to drive significant value for patients with
multiple types of cancer who are in need of new therapy options, and we
look forward to continuing its development with Seattle Genetics.”

Upon closing of the transactions contemplated by the development and
license agreement, Immunomedics would receive an upfront payment of $250
million. In addition, Seattle Genetics would pay development, regulatory
and sales-dependent milestone payments across multiple indications and
geographic regions of up to a total maximum of approximately $1.7
billion, as well as tiered double-digit royalties. The closing of the
transactions contemplated by the development and license agreement is
subject to customary conditions, including the expiration or termination
of the waiting period under the Hart-Scott-Rodino Antitrust Improvements
Act of 1976, as amended. In addition, for a limited period of time,
Immunomedics has the right to continue discussions with a small number
of parties that previously expressed interest in licensing sacituzumab
govitecan. If a third party provides Immunomedics with a financially
superior licensing offer, Seattle Genetics has the right to match any
such offer, and if it decides not to match, Immunomedics has the right
to accept the superior offer and terminate the proposed development and
license agreement upon payment of a termination fee to Seattle Genetics.

Concurrent with the transaction, Seattle Genetics is purchasing
approximately $15 million of common stock, representing a 2.8 percent
stake in Immunomedics. Seattle Genetics has also been granted the right
to purchase an additional 8,655,804 shares of common stock at a price of
$4.90 per share for a defined period. The equity purchase and rights are
not subject to closing of the development and license agreement.

Seattle Genetics’ 2017 financial guidance provided on and as of February
9, 2017 does not take into account the impact of the transactions
contemplated by the development and license agreement or the equity
investment in Immunomedics. Seattle Genetics plans to update its 2017
financial guidance after the closing of the transactions contemplated by
the development and license agreement.

About Sacituzumab Govitecan

Sacituzumab govitecan is an ADC composed of an anti-TROP-2 antibody
linked to SN-38, the active metabolite of irinotecan. TROP-2 is a
cell-surface receptor that is expressed on several tumors, including
cancers of the breast, colon, lung and bladder.

In data reported from a phase 1/2 trial, in 85 evaluable patients with
metastatic TNBC, sacituzumab govitecan showed an objective response rate
of 29 percent and a median duration of response of 10.8 months. For all
89 patients in the intent-to-treat population, the estimated median
overall survival was 18.8 months. Sacituzumab govitecan was generally
well-tolerated. The most common adverse events were nausea, neutropenia,
diarrhea, anemia, vomiting and fatigue.

In 2016, sacituzumab govitecan received Breakthrough Therapy Designation
from the FDA for the treatment of patients with TNBC who have failed
prior therapies for metastatic disease. The regulatory agency has also
granted the ADC Fast Track designation for patients with small-cell lung
cancer (SCLC) or non-small-cell lung cancer (NSCLC). In addition,
sacituzumab govitecan has been designated an orphan drug by the FDA for
the treatment of patients with SCLC or pancreatic cancer and by the
European Medicines Agency (EMA) for the treatment of patients with
pancreatic cancer.

Conference Call Details

Seattle Genetics’ management will host a conference call and webcast to
discuss the transaction today at 5:30 a.m. Pacific Time (PT); 8:30 a.m.
Eastern Time (ET). The live event will be available from the Seattle
Genetics website at www.seattlegenetics.com,
under the Investors and News section, or by calling 800-279-9534
(domestic) or 719-325-2108 (international). The conference ID is
2159368. A replay of the discussion will be available beginning at
approximately 8:30 a.m. PT today from the Seattle Genetics website or by
calling 888-203-1112 (domestic) or 719-457-0820 (international), using
conference ID 2159368. The telephone replay will be available until 5:00
p.m. PT on Monday, February 13, 2017.

About Seattle Genetics

Seattle Genetics is an innovative biotechnology company that develops
and commercializes novel antibody-based therapies for the treatment of
cancer. The company’s industry-leading antibody-drug conjugate (ADC)
technology harnesses the targeting ability of antibodies to deliver
cell-killing agents directly to cancer cells. ADCETRIS^®
(brentuximab vedotin), the company’s lead product, in collaboration with
Takeda Pharmaceutical Company Limited, is the first in a new class of
ADCs and is commercially available globally in 66 countries for relapsed
classical Hodgkin lymphoma (HL) and relapsed systemic anaplastic large
cell lymphoma (sALCL). Seattle Genetics is also advancing vadastuximab
talirine (SGN-CD33A; 33A), an ADC in a phase 3 trial for acute myeloid
leukemia. Headquartered in Bothell, Washington, Seattle Genetics has a
robust pipeline of innovative therapies for blood-related cancers and
solid tumors designed to address significant unmet medical needs and
improve treatment outcomes for patients. The company has collaborations
for its proprietary ADC technology with a number of companies including
AbbVie, Astellas, Bayer, Celldex, Genentech, GlaxoSmithKline and Pfizer.
More information can be found at www.seattlegenetics.com.

Forward-Looking Statements

Certain of the statements made in this press release are forward
looking, such as those, among others, relating to the anticipated
closing of the transactions contemplated by the development and license
agreement and the timing and benefits thereof; the expected future
impacts from, planned regulatory filings relating to and the performance
of, sacituzumab govitecan; the future development, commercial and other
opportunities relating to the licensing of sacituzumab govitecan,
including the expectation of the near-term opportunity to launch a
second drug in the U.S.; and other statements that are not historical
facts. 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, but are not limited to, risks
related to Seattle Genetics’ ability to complete the transactions
contemplated by the development and license agreement on the proposed
terms and schedule, including risks and uncertainties related to the
satisfaction of closing conditions and the possibility that competing
offers by third parties for the licensing of sacituzumab govitecan will
be made; risks associated with licensing transactions, such as the risks
that sacituzumab govitecan will not be integrated into Seattle Genetics’
pipeline successfully or will not perform in clinical testing as
expected, in which case, Seattle Genetics’ may not recover its
investment in sacituzumab govitecan; risks related to future
opportunities and plans for Seattle Genetics and sacituzumab govitecan,
including uncertainty of the expected future regulatory filings and
future development of sacituzumab govitecan; the possibility that if
Seattle Genetics does not complete the transactions contemplated by the
development and license agreement or does not achieve the perceived
benefits of the proposed transaction as rapidly or to the extent
anticipated by financial analysts or investors, the market price of
Seattle Genetics’ common stock could decline; the difficulty and
uncertainty of pharmaceutical product development; the inherent
uncertainty associated with the regulatory approval process, including
the risk that regulatory approval for sacituzumab govitecan in the U.S.
or elsewhere may not be obtained in a timely manner or at all. More
information about the risks and uncertainties faced by Seattle Genetics
is contained in the Company’s quarterly report on Form 10-Q for the
quarter ended September 30, 2016 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.

Contacts

Seattle Genetics, Inc.
Investors:
Peggy Pinkston, 425-527-4160
ppinkston@seagen.com
or
Media:
Brandi
Robinson, 425-527-2910
brobinson@seagen.com