Seattle Genetics to Receive Milestone Payment Under ADC Collaboration with GlaxoSmithKline Following European Commission Approval of BLENREP (belantamab mafodotin)

Seattle Genetics, Inc. (Nasdaq:SGEN) today announced that it will receive a milestone payment from GlaxoSmithKline (GSK) triggered by European Commission conditional marketing authorisation for GSK’s BLENREP™ (belantamab mafodotin), an antibody-drug conjugate (ADC) targeting B-cell maturation antigen (BCMA) that utilizes Seattle Genetics’ proprietary technology. BLENREP was developed and will be commercialized by GSK. In addition to the milestone payment, Seattle Genetics is entitled to royalties on BLENREP product sales. BLENREP was approved as monotherapy for the treatment of multiple myeloma in adult patients who have received at least four prior therapies and whose disease is refractory to at least one proteasome inhibitor, one immunomodulatory agent, and an anti-CD38 monoclonal antibody, and who have demonstrated disease progression on the last therapy.

“This is the second collaborator program utilizing our ADC technology to receive European Commission approval in 2020, and rapidly follows the FDA approval of BLENREP earlier this month, highlighting the potential of these novel therapies in the treatment of cancer patients globally,” said Clay Siegall, Ph.D., President and Chief Executive Officer of Seattle Genetics. “Our ADC collaborator progress, along with the growth of Seattle Genetics’ marketed ADCs, ADCETRIS and PADCEV, and recent positive results of tisotumab vedotin from our ADC pipeline, underscore our leadership in ADCs to treat cancer.”

BLENREP was granted PRIME (PRIority MEdicines) designation in 2017 and the application was reviewed under the European Medicines Agency’s (EMA) accelerated assessment procedure, which is given if the Committee for Medicinal Products for Human Use of the EMA determines the treatment is of major interest from a public health perspective and represents a therapeutic innovation.

Seattle Genetics’ ADC technology combines the specificity of monoclonal antibodies, innovative linker systems and potent cell-killing agents to treat cancer. The technology has been licensed to several companies. Under the terms of these agreements, each licensee company has rights to use the technology with antibodies against specified targets. The licensee is responsible for research, product development, manufacturing and commercialization. Seattle Genetics is entitled to receive fees, progress-dependent milestone payments and royalties on worldwide net sales of any resulting ADC products.

About Seattle Genetics

Seattle Genetics, Inc. is a global biotechnology company that discovers, develops and commercializes transformative cancer medicines to make a meaningful difference in people’s lives. ADCETRIS^® (brentuximab vedotin) and PADCEV^® (enfortumab vedotin-ejfv) use the Company’s industry-leading antibody-drug conjugate (ADC) technology. ADCETRIS is approved in certain CD30-expressing lymphomas, and PADCEV is approved in certain metastatic urothelial cancers. TUKYSA^® (tucatinib), a small molecule tyrosine kinase inhibitor, is approved in certain HER2-positive metastatic breast cancers. The Company is headquartered in the Seattle, Washington area, with locations in California, Switzerland and the European Union. For more information on our robust pipeline, visit www.seattlegenetics.com and follow @SeattleGenetics on Twitter.

Forward-Looking Statements

Certain of the statements made in this press release are forward looking, such as those, among others, relating to anticipated milestone payments, fees, and royalties due to the company from GSK and other licensees, the therapeutic uses of BLENREP, the importance of ADCs in treating cancer and the company’s leadership in the field of ADCs. Actual results or developments may differ materially from those projected or implied in these forward-looking statements due to factors such as unanticipated delays in or other obstacles to the development or commercialization of ADCs subject to these license agreements and the receipt by the Company of consideration from the subject ADC licenses. More information about the risks and uncertainties faced by the Company is contained under the caption “Risk Factors” included in the company’s Quarterly Report on Form 10-Q for the quarter ended June 30, 2020 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.

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