Seattle Genetics Highlights Multiple Data Sets Evaluating the Combination of ADCETRIS® (Brentuximab Vedotin) and Opdivo® (Nivolumab) at ASH Annual Meeting

“Our goal with ADCETRIS is to identify the most effective treatment strategies to improve the outcome of patients, and the combination of ADCETRIS and Opdivo has demonstrated enhanced activity with a tolerable safety profile in Hodgkin lymphoma and now a type of non-Hodgkin lymphoma called primary mediastinal large B-cell lymphoma, or PMBL,” said Roger Dansey, M.D., Chief Medical Officer at Seattle Genetics. “In the Hodgkin lymphoma setting, ADCETRIS plus Opdivo data continue to support investigation of this combination regimen in multiple ongoing studies. The initial data reported from the phase 2 PMBL clinical trial demonstrate a high level of activity of the combination, with an objective response rate of 70 percent and a complete response rate of 27 percent. We and BMS are exploring specific settings where the combination of ADCETRIS and Opdivo has the potential to improve patient outcomes.”

Nivolumab Combined with Brentuximab Vedotin for Relapsed/Refractory Primary Mediastinal Large B-Cell Lymphoma: Preliminary Results from the Phase 2 Checkmate 436 Trial (Abstract #1691, poster presentation on Saturday, December 1, 2018)

Data from the Checkmate 436 phase 2 trial of 30 patients with relapsed or refractory PMBL who received a combination of ADCETRIS plus Opdivo treatment after failure of frontline therapy or autologous stem cell transplant (ASCT) will be presented for the first time. Patients were treated once every three weeks until disease progression or unacceptable toxicity. The median age of patients was 35.5 years. Key findings will be presented in a poster presentation by Alison Moskowitz, M.D., Clinical Director, Lymphoma Inpatient Unit, Memorial Sloan Kettering Cancer Center, New York, and include:

• Of 30 response-evaluable patients, 21 patients (70 percent) had an objective response, including eight patients (27 percent) with a complete response and 13 patients (43 percent) with a partial response, three patients (10 percent) with stable disease, four patients (13 percent) with progressive disease and two patients (seven percent) unable to determine.
• Median time to response was 1.3 months and time to complete response was 3 months. Median duration of response and duration of complete response were not reached.
• The most common adverse events (AEs) of any grade in at least 20 percent of patients were neutropenia (27 percent) and peripheral neuropathy (20 percent). The most common Grade 3 or 4 AEs were neutropenia (27 percent); thrombocytopenia and decreased neutrophil count (seven percent each); and hypersensitivity, diarrhea and maculopapular rash (all three percent). Immune-mediated AEs included diarrhea, maculopapular rash and hyperthyroidism.

Phase 1/2 Study of Brentuximab Vedotin in Combination with Nivolumab in Patients with Relapsed or Refractory Classic Hodgkin Lymphoma: Part 3 (Concurrent Dosing) Results and Updated Progression-Free Survival Results from Parts 1 and 2 (Staggered Dosing) (Abstract #1635, poster presentation on Saturday, December 1, 2018)

Data will be reported from 30 patients with relapsed or refractory HL who received concurrent combination of ADCETRIS plus Opdivo treatment after failure of frontline therapy, representing Part 3 of the study. Patients were treated once every three weeks, with up to four cycles of combination therapy in the outpatient setting. After completion of the fourth cycle of treatment, patients were eligible to undergo an ASCT. The median age of patients was 31.5 years. Data from Parts 1 and 2 of the study were recently reported at the 11^th International Symposium on Hodgkin Lymphoma (ISHL) and can be found here. Key findings will be presented in a poster presentation and include:

• Of 30 response-evaluable patients, 28 patients (93 percent) had an objective response, including 24 patients (80 percent) with a complete response and four patients (13 percent) with a partial response, one patient each (three percent) with stable and progressive disease.
• After a median follow-up time of 12.7 months, the estimated PFS at 12 months was 89 percent.
• The most common AEs of any grade occurring prior to ASCT or subsequent salvage therapy in at least 15 percent of patients were nausea (57 percent), diarrhea and fatigue (37 percent each), vomiting (33 percent), infusion-related reaction (IRR; 30 percent), headache (27 percent), pruritus and pyrexia (23 percent each), and abdominal pain and chills (20 percent each). The majority of IRR AE symptoms were Grade 2 or less and included no treatment discontinuations.

An additional poster will be presented on Monday, December 3, 2018 from the phase 1/2 clinical trial evaluating ADCETRIS in combination with Opdivo in relapsed or refractory HL titled “Baseline Tumor Transcriptome Characteristics Associated with the Response of Relapsed/Refractory Hodgkin Lymphoma Patients to Brentuximab Vedotin in Combination with Nivolumab” (Abstract #2837).

Additional ADCETRIS and Opdivo ASH Data Presentation

The first data will be reported in an oral presentation from the phase 2 CheckMate-744 study, the first risk-stratified, response-adapted study of ADCETRIS and Opdivo, followed by ADCETRIS and bendamustine for suboptimal response, in children, adolescents and young adults with relapsed/refractory classical HL, prior to ASCT. At time of analysis, all evaluable patients achieved complete metabolic remission after completing induction and, as needed, intensification therapy. The most common AEs were nausea (53 percent), diarrhea (31 percent) and pyrexia (28 percent). No AEs led to discontinuation and there were no deaths. Presentation information includes:

• Response-Adapted Therapy with Nivolumab and Brentuximab Vedotin (BV), Followed by BV and Bendamustine for Suboptimal Response, in Children, Adolescents and Young Adults with Standard Risk Relapsed/Refractory Classical Hodgkin Lymphoma (Abstract #927, oral presentation on Monday, December 3, 2018 at 5:00 p.m. PT at the San Diego Convention Center, Room 6F)

About ADCETRIS (brentuximab vedotin)

ADCETRIS is being evaluated broadly in more than 70 clinical trials in CD30-expressing lymphomas. These include three recently completed phase 3 trials: ECHELON-2 in frontline peripheral T-cell lymphomas (also known as mature T-cell lymphoma), ECHELON-1 in previously untreated Hodgkin lymphoma, and ALCANZA in cutaneous T-cell lymphoma. The phase 3 CHECKMATE 812 trial of ADCETRIS in combination with Opdivo (nivolumab) for relapsed/refractory Hodgkin lymphoma is ongoing.

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 injection for intravenous infusion has received FDA approval for six indications in adult patients with: (1) previously untreated systemic anaplastic large cell lymphoma (sALCL) or other CD30-expressing peripheral T-cell lymphomas (PTCL), including angioimmunoblastic T-cell lymphoma and PTCL not otherwise specified, in combination with cyclophosphamide, doxorubicin, and prednisone, (2) previously untreated Stage III or IV classical Hodgkin lymphoma (cHL), in combination with doxorubicin, vinblastine, and dacarbazine, (3) cHL at high risk of relapse or progression as post-autologous hematopoietic stem cell transplantation (auto-HSCT) consolidation, (4) cHL after failure of auto-HSCT or failure of at least two prior multi-agent chemotherapy regimens in patients who are not auto-HSCT candidates, (5) sALCL after failure of at least one prior multi-agent chemotherapy regimen, and (6) primary cutaneous anaplastic large cell lymphoma (pcALCL) or CD30-expressing mycosis fungoides (MF) who have received prior systemic therapy.

Health Canada granted ADCETRIS approval with conditions for relapsed or refractory Hodgkin lymphoma and sALCL in 2013, and non-conditional approval for post-autologous stem cell transplantation (ASCT) consolidation treatment of Hodgkin lymphoma patients at increased risk of relapse or progression.

ADCETRIS received conditional marketing authorization from the European Commission in October 2012. The approved indications in Europe are: (1) for the treatment of adult patients with relapsed or refractory CD30-positive Hodgkin lymphoma following ASCT, or following at least two prior therapies when ASCT or multi-agent chemotherapy is not a treatment option, (2) the treatment of adult patients with relapsed or refractory sALCL, (3) for the treatment of adult patients with CD30-positive Hodgkin lymphoma at increased risk of relapse or progression following ASCT, and (4) for the treatment of adult patients with CD30-positive cutaneous T-cell lymphoma (CTCL) after at least one prior systemic therapy.

ADCETRIS has received marketing authorization by regulatory authorities in 72 countries for relapsed or refractory Hodgkin lymphoma and sALCL. See select important safety information, including Boxed Warning, below.

Seattle Genetics and 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 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. ADCETRIS^® (brentuximab vedotin) utilizes the company’s industry-leading antibody-drug conjugate (ADC) technology and is currently approved for the treatment of multiple CD30-expressing lymphomas. Beyond ADCETRIS, the company has established a pipeline of novel targeted therapies at various stages of clinical testing, including three in ongoing pivotal trials for solid tumors. Enfortumab vedotin for metastatic urothelial cancer and tisotumab vedotin for metastatic cervical cancer utilize our proprietary ADC technology. Tucatinib, a small molecule tyrosine kinase inhibitor, is in a pivotal trial for HER2-positive metastatic breast cancer. In addition, we are leveraging our expertise in empowered antibodies to build a portfolio of proprietary immuno-oncology agents in clinical trials targeting hematologic malignancies and solid tumors. 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.

ADCETRIS (brentuximab vedotin) Important Safety Information

BOXED WARNING: PROGRESSIVE MULTIFOCAL LEUKOENCEPHALOPATHY (PML):

JC virus infection resulting in PML and death can occur in ADCETRIS-treated patients.

Contraindication

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

Warnings and Precautions

• Peripheral neuropathy (PN): ADCETRIS causes PN that is predominantly sensory. Cases of motor PN have also been reported. ADCETRIS-induced PN is cumulative. Monitor for symptoms such as hypoesthesia, hyperesthesia, paresthesia, discomfort, a burning sensation, neuropathic pain, or weakness. Institute dose modifications accordingly.
• Anaphylaxis and infusion reactions: Infusion-related reactions (IRR), including anaphylaxis, have occurred with ADCETRIS. Monitor patients during infusion. If an IRR occurs, interrupt the infusion and institute appropriate medical management. If anaphylaxis occurs, immediately and permanently discontinue the infusion and administer appropriate medical therapy. Premedicate patients with a prior IRR before subsequent infusions. Premedication may include acetaminophen, an antihistamine, and a corticosteroid.
• Hematologic toxicities: Fatal and serious cases of febrile neutropenia have been reported with ADCETRIS. Prolonged (≥1 week) severe neutropenia and Grade 3 or 4 thrombocytopenia or anemia can occur with ADCETRIS. Start primary prophylaxis with G-CSF beginning with Cycle 1 for patients who receive ADCETRIS in combination with chemotherapy for previously untreated Stage III or IV classical HL or previously untreated PTCL. Monitor complete blood counts prior to each ADCETRIS dose. Monitor more frequently 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 ADCETRIS doses.
• Serious infections and opportunistic infections: Infections such as pneumonia, bacteremia, and sepsis or septic shock (including fatal outcomes) have been reported in ADCETRIS-treated patients. Closely monitor patients during treatment for 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 use 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 use in patients with moderate or severe hepatic impairment.
• Hepatotoxicity: Fatal and serious cases have occurred in ADCETRIS-treated patients. Cases were consistent with hepatocellular injury, including elevations of transaminases and/or bilirubin, and occurred after the first ADCETRIS dose or rechallenge. Preexisting liver disease, elevated baseline liver enzymes, and concomitant medications may increase the risk. Monitor liver enzymes and bilirubin. Patients with new, worsening, or recurrent hepatotoxicity may require a delay, change in dose, or discontinuation of ADCETRIS.
• PML: Fatal cases of JC virus infection resulting in PML and death have 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. Other possible contributory factors other than ADCETRIS include prior therapies and underlying disease that may cause immunosuppression. Consider PML diagnosis in patients 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: Fatal and serious events of noninfectious pulmonary toxicity including pneumonitis, interstitial lung disease, and acute respiratory distress syndrome have been reported. Monitor patients for signs and symptoms, 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: Fatal and serious cases of Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) have been reported with ADCETRIS. If SJS or TEN occurs, discontinue ADCETRIS and administer appropriate medical therapy.
• Gastrointestinal (GI) complications: Fatal and serious cases of acute pancreatitis have been reported. Other fatal and serious GI complications include perforation, hemorrhage, erosion, ulcer, intestinal obstruction, enterocolitis, neutropenic colitis, and ileus. Lymphoma with preexisting GI involvement may increase the risk of perforation. In the event of new or worsening GI symptoms, perform a prompt diagnostic evaluation and treat appropriately.
• Embryo-fetal toxicity: Based on the mechanism of action and animal studies, ADCETRIS can cause fetal harm. Advise females of reproductive potential of the potential risk to the fetus, and to avoid pregnancy during ADCETRIS treatment and for at least 6 months after the final dose of ADCETRIS.

Most Common (≥20% in any study) Adverse Reactions: Peripheral neuropathy, fatigue, nausea, diarrhea, neutropenia, upper respiratory tract infection, pyrexia, constipation, vomiting, alopecia, decreased weight, abdominal pain, anemia, stomatitis, lymphopenia and mucositis.

Drug Interactions

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

Use in Specific Populations

Moderate or severe hepatic impairment or severe renal impairment: MMAE exposure and adverse reactions are increased. Avoid use.

Advise males with female sexual partners of reproductive potential to use effective contraception during ADCETRIS treatment and for at least 6 months after the final dose of ADCETRIS.

Advise patients to report pregnancy immediately and avoid breastfeeding while receiving ADCETRIS.

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

Seattle Genetics Forward-Looking Statements

Certain of the statements made in this press release are forward-looking, such as those, among others, relating to the potential utilization of ADCETRIS (brentuximab vedotin) in treatment settings and in combination with Opdivo and other agents which have not received regulatory approval. Actual results or developments may differ materially from those projected or implied in these forward-looking statements due to factors such as that ADCETRIS may not receive regulatory approval for use in the treatment settings and in combination with Opdivo and other agents as referenced, competitive conditions including the availability of alternative treatment regimens, the availability and extent of reimbursement, the risk of adverse events, and adverse regulatory action. More information about the risks and uncertainties faced by Seattle Genetics is contained under the caption “Risk Factors” included in the company’s Quarterly Report on Form 10-Q for the quarter ended September 30, 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.

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