- After Median Follow-Up of 11.5 Months, 73 Percent of Patients Had Confirmed Tumor Response with Majority of Responses Still Ongoing; No New Safety Signals Observed for the Combination -

- Findings To Be Presented During an Oral Session at the 2020 Genitourinary Cancers Symposium -

BOTHELL, Wash. and TOKYO, Feb. 10, 2020 /PRNewswire/ --Seattle Genetics, Inc.(Nasdaq: SGEN) and Astellas Pharma Inc.(TSE: 4503, President and CEO: Kenji Yasukawa, Ph.D., "Astellas") today announced updated results from the phase 1b/2 clinical trial EV-103 in previously untreated patients with locally advanced or metastatic urothelial cancer who were ineligible for treatment with cisplatin-based chemotherapy. Forty-five patients were treated with the combination of PADCEV (enfortumab vedotin-ejfv) and pembrolizumab and were evaluated for safety and efficacy. After a median follow-up of 11.5 months, the study results continue to meet outcome measures for safety and demonstrate encouraging clinical activity for this platinum-free combination in a first-line setting. Updated results will be presented during an oral session on Friday, February 14 at the 2020 Genitourinary Cancers Symposium in San Francisco (Abstract #441). Initial results from the study were presented at the European Society of Medical Oncology Congress in September 2019.

PADCEV is a first-in-class antibody-drug conjugate (ADC) that is directed against Nectin-4, a protein located on the surface of cells and highly expressed in bladder cancer.1,2

"Cisplatin-basedchemotherapy is the standard treatment for first-line advanced urothelial cancer; however, it isn't an option for many patients,"said Jonathan E. Rosenberg, M.D., Medical Oncologist and Chief, Genitourinary Medical Oncology Service at Memorial Sloan Kettering Cancer Center in New York."I'm encouraged by these interim results, including a median progression-free survival of a year for patients who received the platinum-free combination of PADCEV and pembrolizumab in the first-line setting."

In the study, 58 percent (26/45) of patients had a treatment-related adverse event greater than or equal to Grade 3: increase in lipase (18 percent; 8/45), rash (13 percent; 6/45), hyperglycemia (13 percent; 6/45) and peripheral neuropathy (4 percent; 2/45); these rates were similar to those observed with PADCEV monotherapy.3Eighteen percent (8/45) of patients had treatment-related immune-mediated adverse events of clinical interest greater than or equal to Grade 3 that required the use of systemic steroids (arthralgia, dermatitis bullous, pneumonitis, lipase increased, rash erythematous, rash maculo-papular, tubulointerstitial nephritis, myasthenia gravis). None of the adverse events of clinical interest were Grade 5 events. Six patients (13 percent) discontinued treatment due to treatment-related adverse events, most commonly peripheral sensory neuropathy. As previously reported, there was one death deemed to be treatment-related by the investigator attributed to multiple organ dysfunction syndrome.

The data demonstrated the combination of PADCEV plus pembrolizumab shrank tumors in the majority of patients, resulting in a confirmed objective response rate (ORR) of 73.3 percent (33/45; 95% Confidence Interval (CI): 58.1, 85.4) after a median follow-up of 11.5 months (range,0.7 to 19.2). Responses included 15.6 percent (7/45) of patients who had a complete response (CR)and 57.8 percent (26/45) of patients who had a partial response. Median duration of response has not yet been reached (range 1.2 to 12.9+ months). Eighteen (55%) of 33 responses were ongoing at the time of analysis, with 83.9% of responses lasting at least 6 months and 53.7% of responses lasting at least 12 months (Kaplan-Meier estimate).The median progression-free survival was 12.3 months (95% CI: 7.98, -) and the 12-month overall survival (OS) rate was 81.6 percent (95% CI: 62 to 91.8 percent); median OS has not been reached.

"These updated data are encouraging and provide support for the recently initiated phase 3 trial EV-302 that includes an arm evaluating PADCEV in this platinum-free combination in the first-line setting," said Roger Dansey, M.D., Chief Medical Officer at Seattle Genetics.

"These additional results support continued evaluation of PADCEV in combination with other agents and at earlier stages of treatment for patients withurothelial cancer," said Andrew Krivoshik, M.D., Ph.D., Senior Vice President and Oncology Therapeutic Area Head at Astellas.

About the EV-103 TrialEV-103 is an ongoing, multi-cohort, open-label, multicenter phase 1b/2 trial of PADCEV alone or in combination, evaluating safety, tolerability and efficacy in muscle invasive, locally advanced and first- and second-line metastatic urothelial cancer.

The dose-escalation cohort and expansion cohort A include locally advanced or metastatic urothelial cancer patients who are ineligible for cisplatin-based chemotherapy. Patients were dosed in a 21-day cycle, receiving an intravenous (IV) infusion of enfortumab vedotin on Days 1 and 8 and pembrolizumab on Day 1. At the time of this initial analysis, 45 patients (5 from the dose-escalation cohort and 40 from the dose-expansion cohort A) with locally advanced and/or metastatic urothelial cancer had been treated with enfortumab vedotin (1.25 mg/kg) plus pembrolizumab in the first-line setting.

The primary outcome measure of the cohorts included in this analysis is safety. Key secondary objectives related to efficacy include objective response rate (ORR), disease control rate (DCR), duration of response (DoR), progression free survival (PFS) and overall survival (OS). DoR,PFS and OS are not yet mature.

Additional cohorts in the EV-103 study will evaluate enfortumab vedotin:

More information about PADCEV clinical trials can be found at clinicaltrials.gov.

About Bladder and Urothelial CancerIt is estimated that approximately 81,000 people in the U.S. will be diagnosed with bladder cancer in 2020.5 Urothelial cancer accounts for 90 percent of all bladder cancers and can also be found in the renal pelvis, ureter and urethra.6 Globally, approximately 549,000 people were diagnosed with bladder cancer in 2018, and there were approximately 200,000 deaths worldwide.7

The recommended first-line treatment for patients with advanced urothelial cancer is a cisplatin-based chemotherapy. For patients who are ineligible for cisplatin, such as people with kidney impairment, a carboplatin-based regimen is recommended. However, fewer than half of patients respond to carboplatin-based regimens and outcomes are typically poorer compared to cisplatin-based regimens.8

About PADCEV PADCEV (enfortumabvedotin-ejfv) was approved by the U.S. Food and Drug Administration (FDA) in December 2019 and is indicated for the treatment of adult patients with locally advanced or metastatic urothelial cancer who have previously received a programmed death receptor-1 (PD-1) or programmed death-ligand 1 (PD-L1) inhibitor and a platinum-containing chemotherapy before (neoadjuvant) or after (adjuvant) surgery or in a locally advanced or metastatic setting. PADCEV was approved under the FDA's Accelerated Approval Program based on tumor response rate. Continued approval may be contingent upon verification and description of clinical benefit in confirmatory trials.9

PADCEV is a first-in-class antibody-drug conjugate (ADC) that is directed against Nectin-4, a protein located on the surface of cells and highly expressed in bladder cancer.2,9Nonclinical data suggest the anticancer activity of PADCEV is due to its binding to Nectin-4 expressing cells followed by the internalization and release of the anti-tumor agent monomethyl auristatin E (MMAE) into the cell, which result in the cell not reproducing (cell cycle arrest) and in programmed cell death (apoptosis).9PADCEV is co-developed by Astellas and Seattle Genetics.

Important Safety Information

Warnings and Precautions

Adverse ReactionsSerious adverse reactions occurred in 46% of patients treated with PADCEV. The most common serious adverse reactions (3%) were urinary tract infection (6%), cellulitis (5%), febrile neutropenia (4%), diarrhea (4%), sepsis (3%), acute kidney injury (3%), dyspnea (3%), and rash (3%). Fatal adverse reactions occurred in 3.2% of patients, including acute respiratory failure, aspiration pneumonia, cardiac disorder, and sepsis (each 0.8%).

Adverse reactions leading to discontinuation occurred in 16% of patients; the most common adverse reaction leading to discontinuation was peripheral neuropathy (6%). Adverse reactions leading to dose interruption occurred in 64% of patients; the most common adverse reactions leading to dose interruption were peripheral neuropathy (18%), rash (9%) and fatigue (6%). Adverse reactions leading to dose reduction occurred in 34% of patients; the most common adverse reactions leading to dose reduction were peripheral neuropathy (12%), rash (6%) and fatigue (4%).

The most common adverse reactions (20%) were fatigue (56%), peripheral neuropathy (56%), decreased appetite (52%), rash (52%), alopecia (50%), nausea (45%), dysgeusia (42%), diarrhea (42%), dry eye (40%), pruritus (26%) and dry skin (26%). The most common Grade 3 adverse reactions (5%) were rash (13%), diarrhea (6%) and fatigue (6%).

Lab AbnormalitiesIn one clinical trial, Grade 3-4 laboratory abnormalities reported in 5% were: lymphocytes decreased, hemoglobin decreased, phosphate decreased, lipase increased, sodium decreased, glucose increased, urate increased, neutrophils decreased.

Drug Interactions

Specific Populations

For more information, please see the full Prescribing Information for PADCEV here.

About Seattle GeneticsSeattle Genetics, Inc. is a global biotechnology company that discovers, develops and commercializes transformative medicines targeting cancer to make a meaningful difference in people's lives. The company is headquartered in Bothell, Washington, and has offices in California, Switzerland and the European Union. For more information on our robust pipeline, visit https://www.seattlegenetics.comand follow @SeattleGenetics on Twitter.

About AstellasAstellas 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 CollaborationSeattle Genetics and Astellas are co-developing enfortumab vedotin-ejfv 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 StatementsCertain statements made in this press release are forward looking, such as those, among others, relating to the EV-103 and EV-302 clinical trials; clinical development plans relating to enfortumab vedotin; the therapeutic potential of enfortumab vedotin; and its possible safety, efficacy, and therapeutic uses, including in the first-line setting. 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 possibility that ongoing and subsequent clinical trials of enfortumab vedotin may fail to establish sufficient efficacy; that adverse events or safety signals may occur and that adverse regulatory actions or other setbacks could occur 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, 2019 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, except as required by law.

Astellas Cautionary NotesIn 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 PADCEV [package insert]. Northbrook, IL: Astellas, Inc.2 Challita-Eid P, Satpayev D, Yang P, et al. Enfortumab Vedotin Antibody-Drug Conjugate Targeting Nectin-4 Is a Highly Potent Therapeutic Agent in Multiple Preclinical Cancer Models. Cancer Res 2016;76(10):3003-13.3 Rosenberg JE, O'Donnell PH, Balar AV, et al. Pivotal Trial of Enfortumab Vedotin in Urothelial Carcinoma After Platinum and Anti-Programmed Death 1/Programmed Death Ligand 1 Therapy. J Clin Oncol 2019;37(29):2592-600.4 ClinicalTrials.gov. A Study of Enfortumab Vedotin Alone or With Other Therapies for Treatment of Urothelial Cancer (EV-103). https://clinicaltrials.gov/ct2/show/NCT03288545.5 American Cancer Society. Cancer Facts & Figures 2020. https://www.cancer.org/content/dam/cancer-org/research/cancer-facts-and-statistics/annual-cancer-facts-and-figures/2020/cancer-facts-and-figures-2020.pdf. Accessed 01-23-2020.6National Cancer Institute. Surveillance, Epidemiology, and End Results Program. Cancer stat facts: bladder cancer. https://seer.cancer.gov/statfacts/html/urinb.html. Accessed 05-01-2019.7International Agency for Research on Cancer. Cancer Tomorrow: Bladder. http://gco.iarc.fr/tomorrow. 8 National Comprehensive Cancer Network (NCCN). NCCN Clinical Practice Guidelines in Oncology: Bladder Cancer. Version 4; July 10, 2019. https://www.nccn.org/professionals/physician_gls/pdf/bladder.pdf.9 PADCEV [package insert]. Northbrook, IL: Astellas, Inc.

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Seattle Genetics and Astellas Announce Updated Results from Phase 1b/2 Trial of PADCEV (enfortumab vedotin-ejfv) in Combination with Immune Therapy...