Seattle Genetics Announces Initiation of Phase 1/2 Clinical Trial of ADCETRIS® (Brentuximab Vedotin) in Combination with Opdivo® (Nivolumab) in Second-line Hodgkin Lymphoma

Seattle Genetics, Inc. (Nasdaq:SGEN) today announced that it has initiated a phase 1/2 clinical trial of ADCETRIS (brentuximab vedotin) in combination with Opdivo (nivolumab) for patients with relapsed or refractory Hodgkin lymphoma (HL) after failure of frontline treatment. The trial is being conducted under a previously announced clinical trial collaboration agreement with Bristol-Myers Squibb Company (NYSE:BMY). ADCETRIS is an antibody-drug conjugate (ADC) directed to CD30, a defining marker of classical HL, which combines the targeting ability of a monoclonal antibody with a highly potent cell-killing agent. Opdivo is a human antibody that targets and inhibits the programmed death receptor-1 (PD-1), resulting in T-cell activation. Opdivo is part of a new class of cancer immunotherapy treatments known as checkpoint inhibitors, which are designed to harness the body’s own immune system in fighting cancer by targeting distinct regulatory components of the immune system. A second trial under the collaboration is planned to begin later in 2015 for relapsed or refractory B-cell and T-cell non-Hodgkin lymphoma (NHL), including diffuse large B-cell lymphoma (DLBCL).

“This is the first corporate-sponsored clinical trial to evaluate ADCETRIS combined with a checkpoint inhibitor to determine if the combination can improve patient outcomes,” said Jonathan Drachman, M.D., Chief Medical Officer and Executive Vice President, Research and Development. “The trial supports our strategy to establish ADCETRIS as the foundation of care for CD30-expressing malignancies, and to test novel combinations that could benefit patients. We are executing a broad clinical program with ADCETRIS to potentially expand into earlier lines of therapy and new indications, including the ECHELON-1 trial in frontline Hodgkin lymphoma, the ECHELON-2 trial in frontline mature T-cell lymphoma, the ALCANZA trial in cutaneous T-cell lymphoma and both ongoing and planned trials in diffuse large B-cell lymphoma.”

The phase 1/2 open-label trial will enroll relapsed or refractory HL patients who have failed frontline therapy. The primary objective is to assess the safety and antitumor activity of ADCETRIS in combination with Opdivo. After completion of four cycles of combination therapy, patients are eligible to undergo autologous stem cell transplant (ASCT). Patients at high risk of relapse or progression following ASCT will be eligible to receive ADCETRIS in the commercial setting. All patients will be assessed for progression-free survival after ASCT. The trial is being conducted at multiple centers in the United States and is designed to enroll up to approximately 60 patients.

ADCETRIS is not currently approved for the treatment of second-line, transplant eligible HL or for the treatment of NHL other than relapsed systemic anaplastic large cell lymphoma. Opdivo is currently not approved for the treatment of lymphoma.

About ADCETRIS^® (Brentuximab Vedotin)

ADCETRIS is an ADC comprising an anti-CD30 monoclonal antibody attached by a protease-cleavable linker to a microtubule disrupting agent, monomethyl auristatin E (MMAE), utilizing Seattle Genetics’ proprietary technology. The ADC employs a linker system that is designed to be stable in the bloodstream but to release MMAE upon internalization into CD30-expressing tumor cells.

ADCETRIS for intravenous injection has received approval from the FDA for three indications: (1) regular approval for the treatment of patients with classical HL after failure of autologous hematopoietic stem cell transplantation (auto-HSCT) or after failure of at least two prior multi-agent chemotherapy regimens in patients who are not auto-HSCT candidates, (2) regular approval for the treatment of classical HL patients at high risk of relapse or progression as post-auto-HSCT consolidation, and (3) accelerated approval for the treatment of patients with systemic anaplastic large cell lymphoma (sALCL) after failure of at least one prior multi-agent chemotherapy regimen. The sALCL indication is approved under accelerated approval based on overall response rate. Continued approval for the sALCL indication may be contingent upon verification and description of clinical benefit in confirmatory trials. Health Canada granted ADCETRIS approval with conditions for relapsed or refractory HL and sALCL.

ADCETRIS was granted conditional marketing authorization by the European Commission in October 2012 for two indications: (1) for the treatment of adult patients with relapsed or refractory CD30-positive HL following autologous stem cell transplant (ASCT), or following at least two prior therapies when ASCT or multi-agent chemotherapy is not a treatment option, and (2) the treatment of adult patients with relapsed or refractory sALCL. ADCETRIS has received marketing authorization by regulatory authorities in more than 55 countries. See important safety information below.

Seattle Genetics and Takeda Pharmaceutical Company Limited (Takeda) are jointly developing ADCETRIS. Under the terms of the collaboration agreement, Seattle Genetics has U.S. and Canadian commercialization rights and Takeda has rights to commercialize ADCETRIS in the rest of the world. Seattle Genetics and Takeda are funding joint development costs for ADCETRIS on a 50:50 basis, except in Japan where Takeda is solely responsible for development costs.

About Lymphoma

Lymphoma is a general term for a group of cancers that originate in the lymphatic system. There are two major categories of lymphoma: HL and NHL. HL is distinguished from other types of lymphoma by the presence of one characteristic type of cell, known as the Reed-Sternberg cell. The Reed-Sternberg cell generally expresses CD30. NHL is further categorized into indolent (low-grade) or aggressive, including DLBCL. DLBCL is the most common type of NHL.

About Seattle Genetics

Seattle Genetics is a biotechnology company focused on the development and commercialization of innovative antibody-based therapies for the treatment of cancer. Seattle Genetics is leading the field in developing antibody-drug conjugates (ADCs), a technology designed to harness the targeting ability of antibodies to deliver cell-killing agents directly to cancer cells. The company’s lead product, ADCETRIS^® (brentuximab vedotin) is a CD30-targeted ADC that, in collaboration with Takeda Pharmaceutical Company Limited, is commercially available in more than 55 countries, including the U.S., Canada, Japan and members of the European Union. Additionally, ADCETRIS is being evaluated broadly in more than 30 ongoing clinical trials in CD30-expressing malignancies. Seattle Genetics is also advancing a robust pipeline of clinical-stage programs, including SGN-CD19A, SGN-CD33A, SGN-LIV1A, SGN-CD70A, ASG-22ME, ASG-15ME and SEA-CD40. Seattle Genetics has collaborations for its ADC technology with a number of leading biotechnology and pharmaceutical companies, including AbbVie, Agensys (an affiliate of Astellas), Bayer, Genentech, GlaxoSmithKline and Pfizer. More information can be found at www.seattlegenetics.com.

ADCETRIS (brentuximab vedotin) U.S. Important Safety Information

BOXED WARNING

Progressive multifocal leukoencephalopathy (PML): JC virus infection resulting in PML and death can occur in patients receiving ADCETRIS^® (brentuximab vedotin).

Contraindication

ADCETRIS is contraindicated with concomitant bleomycin due to pulmonary toxicity (e.g., interstitial infiltration and/or inflammation).

Warnings and Precautions

• Peripheral neuropathy: ADCETRIS treatment causes a peripheral neuropathy that is predominantly sensory. Cases of peripheral motor neuropathy have also been reported. ADCETRIS-induced peripheral neuropathy is cumulative. Monitor patients for symptoms of neuropathy, such as hypoesthesia, hyperesthesia, paresthesia, discomfort, a burning sensation, neuropathic pain or weakness and institute dose modifications accordingly.
• Anaphylaxis and infusion reactions: Infusion-related reactions, including anaphylaxis, have occurred with ADCETRIS. Monitor patients during infusion. If an infusion-related reaction occurs, interrupt the infusion and institute appropriate medical management. If anaphylaxis occurs, immediately and permanently discontinue the infusion and administer appropriate medical therapy.
• Hematologic toxicities: Prolonged (≥1 week) severe neutropenia and Grade 3 or 4 thrombocytopenia or anemia can occur with ADCETRIS. Febrile neutropenia has been reported with ADCETRIS. Monitor complete blood counts prior to each dose of ADCETRIS and consider more frequent monitoring for patients with Grade 3 or 4 neutropenia. Monitor patients for fever. If Grade 3 or 4 neutropenia develops, consider dose delays, reductions, discontinuation, or G-CSF prophylaxis with subsequent doses.
• Serious infections and opportunistic infections: Infections such as pneumonia, bacteremia, and sepsis or septic shock (including fatal outcomes) have been reported in patients treated with ADCETRIS. Closely monitor patients during treatment for the emergence of possible bacterial, fungal or viral infections.
• Tumor lysis syndrome: Closely monitor patients with rapidly proliferating tumor and high tumor burden.
• Increased toxicity in the presence of severe renal impairment: The frequency of ≥Grade 3 adverse reactions and deaths was greater in patients with severe renal impairment compared to patients with normal renal function. Avoid the use of ADCETRIS in patients with severe renal impairment.
• Increased toxicity in the presence of moderate or severe hepatic impairment: The frequency of ≥Grade 3 adverse reactions and deaths was greater in patients with moderate or severe hepatic impairment compared to patients with normal hepatic function. Avoid the use of ADCETRIS in patients with moderate or severe hepatic impairment.
• Hepatotoxicity: Serious cases of hepatotoxicity, including fatal outcomes, have occurred with ADCETRIS. Cases were consistent with hepatocellular injury, including elevations of transaminases and/or bilirubin, and occurred after the first dose of ADCETRIS or rechallenge. Preexisting liver disease, elevated baseline liver enzymes, and concomitant medications may also increase the risk. Monitor liver enzymes and bilirubin. Patients experiencing new, worsening, or recurrent hepatotoxicity may require a delay, change in dose, or discontinuation of ADCETRIS.
• Progressive multifocal leukoencephalopathy (PML): JC virus infection resulting in PML and death has been reported in ADCETRIS-treated patients. First onset of symptoms occurred at various times from initiation of ADCETRIS therapy, with some cases occurring within 3 months of initial exposure. In addition to ADCETRIS therapy, other possible contributory factors include prior therapies and underlying disease that may cause immunosuppression. Consider the diagnosis of PML in any patient presenting with new-onset signs and symptoms of central nervous system abnormalities. Hold ADCETRIS if PML is suspected and discontinue ADCETRIS if PML is confirmed.
• Pulmonary Toxicity: Events of noninfectious pulmonary toxicity including pneumonitis, interstitial lung disease, and acute respiratory distress syndrome, some with fatal outcomes, have been reported. Monitor patients for signs and symptoms of pulmonary toxicity, including cough and dyspnea. In the event of new or worsening pulmonary symptoms, hold ADCETRIS dosing during evaluation and until symptomatic improvement.
• Serious dermatologic reactions: Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN), including fatal outcomes, have been reported with ADCETRIS. If SJS or TEN occurs, discontinue ADCETRIS and administer appropriate medical therapy.
• Embryo-fetal toxicity: Fetal harm can occur. Advise pregnant women of the potential hazard to the fetus.

Most Common Adverse Reactions:

ADCETRIS was studied as monotherapy in 160 patients with relapsed classical HL and sALCL in two uncontrolled single-arm trials. Across both trials, the most common adverse reactions (≥20%), regardless of causality, were neutropenia, peripheral sensory neuropathy, fatigue, nausea, anemia, upper respiratory tract infection, diarrhea, pyrexia, rash, thrombocytopenia, cough and vomiting.

ADCETRIS was studied in 329 patients with classical HL at high risk of relapse or progression post-auto-HSCT in a placebo-controlled randomized trial. The most common adverse reactions (≥20%) in the ADCETRIS-treatment arm (167 patients), regardless of causality, were neutropenia, peripheral sensory neuropathy, thrombocytopenia, anemia, upper respiratory tract infection, fatigue, peripheral motor neuropathy, nausea, cough, and diarrhea.

Drug Interactions:

Concomitant use of strong CYP3A4 inhibitors or inducers, or P-gp inhibitors, has the potential to affect the exposure to monomethyl auristatin E (MMAE).

Use in Specific Populations:

MMAE exposure and adverse reactions are increased in patients with moderate or severe hepatic impairment or severe renal impairment. Avoid use.

For additional Important Safety Information, including Boxed WARNING, please see the full Prescribing Information for ADCETRIS at http://www.seattlegenetics.com/pdf/adcetris_USPI.pdf.

Forward-Looking Statements

Certain of the statements made in this press release are forward-looking, such as those, among others, relating to the future potential therapeutic uses of ADCETRIS (including in combination with Opdivo) and future clinical and regulatory progress. 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 risks related to adverse clinical results associated with the use of ADCETRIS or Opdivo (or the combination), the failure of the companies to continue their collaboration or execute on the planned clinical trials or adverse regulatory action. More information about the risks and uncertainties faced by Seattle Genetics is contained under the caption “Risk Factors” included in Exhibit 99.1 to the company’s Current Report on Form 8-K filed with the Securities and Exchange Commission on September 9, 2015. 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.

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