Seattle Genetics Highlights Data Presentations from Genentech ADC Collaborator Programs at ASH Annual Meeting

  Seattle Genetics Highlights Data Presentations from Genentech ADC
  Collaborator Programs at ASH Annual Meeting

 -Encouraging Phase I Data from Two ADC Programs Utilizing Seattle Genetics’
                                 Technology-

54th American Society of Hematology (ASH) Annual Meeting and Exposition

Business Wire

ATLANTA -- December 11, 2012

Seattle Genetics, Inc. (Nasdaq:SGEN) today highlighted clinical data from two
antibody-drug conjugate (ADC) programs in development by Genentech, a member
of the Roche Group (SIX: RO, ROG; OTCQX: RHHBY) that utilize Seattle Genetics’
technology. The data were presented at the 54^th American Society of
Hematology (ASH) Annual Meeting and Exposition being held December 8-11, 2012
in Atlanta, GA. Phase I data from both ADCs, an anti-CD22 ADC (DCDT2980S,
RG7593) and an anti-CD79b ADC (DCDS4501A, RG7596), demonstrated antitumor
activity in relapsed or refractory B-cell non-Hodgkin lymphoma (NHL) patients
at generally well-tolerated doses. These ADC programs are currently being
evaluated in a phase II clinical trial for patients with relapsed or
refractory B-cell NHL.

“Genentech’s phase I data and their advancement of these two ADCs into phase
II clinical development, as well as their utilization of our technology in six
other clinical-stage programs,illustrates their commitment to ADCs as an
innovative, targeted approach to treat cancer,”saidEric Dobmeier,
ChiefOperatingOfficer of Seattle Genetics. “Across our ADC collaborations,
there is broad potential for our industry-leading technologyto address
thesignificant needformore effective and better tolerated treatment
options.”

Anti-CD22-MMAE and anti-CD79b-MMAE are ADCs designed to deliver potent
cytotoxic treatment to targeted cells with improved tolerability. With over a
decade of experience and knowledge in ADC innovation, Seattle Genetics has
developed proprietary technology employing synthetic cytotoxic agents, such as
monomethyl auristatin E (MMAE), and stable linker systems that attach these
cytotoxic agents to the antibody. Seattle Genetics’ linker systems are
designed to be stable in the bloodstream and release the potent cell-killing
agent once inside targeted cancer cells. This approach is intended to spare
non-targeted cells and thus reduce many of the toxic effects of traditional
chemotherapy while enhancing antitumor activity. ADCETRIS^® (brentuximab
vedotin) is the first drug approved utilizing Seattle Genetics’ ADC
technology.

A Phase I Study of the Anti-CD79b Antibody-Drug Conjugate (ADC) DCDS4501A
Targeting CD79b in Relapsed or Refractory B-Cell Non-Hodgkin’s Lymphoma
(Abstract #56)

A phase I clinical trial is being conducted to evaluate the safety and
activity of DCDS4501A in patients with relapsed or refractory B-cell NHL.
DCDS4501A is an ADC consisting of an anti-CD79b monoclonal antibody conjugated
to the cytotoxic agent MMAE using Seattle Genetics’ ADC technology. In this
analysis, 47 patients were evaluable for safety and 32 were evaluable for
efficacy.

Key findings included:

  *Patients enrolled in the study were diagnosed with a variety of types of
    B-cell NHL, including diffuse large B-cell lymphoma (DLBCL), follicular
    lymphoma, mantle cell lymphoma and marginal zone lymphoma. All patients
    had relapsed or refractory disease and were heavily pretreated, with a
    median of four prior systemic therapies. Ninety-six percent of patients
    had received prior rituximab and 29 percent had received a prior
    autologous stem cell transplant (ASCT). The median age of patients
    enrolled was 64.
  *Patients received doses ranging from 0.1 milligrams per kilogram (mg/kg)
    to 2.4 mg/kg on an every three week basis, and 2.4 mg/kg was selected as
    the recommended phase II dose.
  *Among all 32 patients evaluable for efficacy, ten patients (31 percent)
    had an objective response to single-agent DCDS4501A. Among the 17 patients
    treated at doses greater than or equal to 1.8 mg/kg, eight patients (47
    percent) had an objective response.
  *The most common adverse events were neutropenia, diarrhea, fever, nausea,
    fatigue, anemia, hyperglycemia and thrombocytopenia. Most adverse events
    were Grade 1 or 2.
  *The most common Grade 3 or 4 adverse events were neutropenia,
    thrombocytopenia, anemia and leukopenia.

A Phase I Study of DCDT2980S, an Antibody-Drug Conjugate (ADC) Targeting CD22,
in Relapsed or Refractory B-Cell Non-Hodgkin’s Lymphoma (Abstract #59)

A phase I clinical trial is being conducted to evaluate the safety and
activity of DCDT2980S in patients with relapsed or refractory B-cell NHL.
DCDT2980S is an ADC candidate consisting of an anti-CD22 monoclonal antibody
conjugated to the cytotoxic agent MMAE using Seattle Genetics’ ADC technology.
In this analysis, 43 patients were evaluable for safety and 33 were evaluable
for efficacy.

Key findings included:

  *Patients enrolled in the study were diagnosed with a variety of types of
    B-cell NHL, including DLBCL, follicular lymphoma, transformed follicular
    lymphoma and small lymphocytic lymphoma. All patients had relapsed or
    refractory disease and were heavily pretreated, with a median of four
    prior systemic therapies. All patients had received prior rituximab and 16
    percent had received a prior autologous stem cell transplant. The median
    age of patients enrolled was 66.
  *Patients received doses ranging from 0.1 mg/kg up to 3.2 mg/kg on an every
    three week basis, and 2.4 mg/kg was selected as the recommended phase II
    dose.
  *Among all 33 patients evaluable for efficacy, nine patients (27 percent)
    had an objective response to single-agent DCDT2980S. Among the 17 patients
    treated at doses greater than or equal to 1.8 mg/kg, seven patients (41
    percent) had an objective response, including one complete response and
    six partial responses.
  *The most common adverse events were fatigue, diarrhea, nausea, neutropenia
    and decreased appetite. Most adverse events were Grade 1 or 2.
  *The most common Grade 3 or 4 adverse events were neutropenia, anemia,
    diarrhea and peripheral neuropathy.

A randomized phase II trial evaluating both DCDS4501A and DCDT2980S in
combination with rituximab for relapsed or refractory B-cell NHL is currently
enrolling. This trial is designed to enroll up to 120 patients at 40 clinical
sites in North America and Europe. For more information about the trial, visit
www.clinicaltrials.gov.

About Seattle Genetics

Seattle Genetics is a biotechnology company focused on the development and
commercialization of monoclonal antibody-based therapies for the treatment of
cancer. The U.S. Food and Drug Administration granted accelerated approval of
ADCETRIS in August 2011 for two indications. ADCETRIS is being developed in
collaboration with Millennium: The Takeda Oncology Company. In addition,
Seattle Genetics has three other clinical-stage ADC programs: SGN-75, ASG-5ME
and ASG-22ME. Seattle Genetics has collaborations for its ADC technology with
a number of leading biotechnology and pharmaceutical companies, including
Abbott, Agensys (an affiliate of Astellas), Bayer, Celldex Therapeutics,
Daiichi Sankyo, Genentech, GlaxoSmithKline, Millennium, Pfizer and Progenics,
as well as ADC co-development agreements with Agensys and Genmab. More
information can be found at www.seattlegenetics.com.

Certain of the statements made in this press release are forward looking, such
as those, among others, relating to the therapeutic potential of our
collaborators ADCs. 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 the risk of adverse events as these ADCs
advance in clinical trials. More information about the risks and uncertainties
faced by Seattle Genetics is contained in the company’s 10-Q for the quarter
ended September 30, 2012 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.

Contact:

Seattle Genetics, Inc.
Investors:
Peggy Pinkston, +1-425-527-4160
ppinkston@seagen.com
or
Media:
Tricia Larson, +1-425-527-4180
tlarson@seagen.com
 
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