Phase 3 Trial of ADCETRIS® (brentuximab vedotin) with Modified Chemo Regimen Shows Non-Inferiority with Unprecedented 3-Year Progression Free Survival of 94.9% vs Less Tolerable International Standard of Care in Advanced Classical Hodgkin Lymphoma

– Results are from 1,500 patient trial conducted by German Hodgkin Study Group to test ADCETRIS regimen versus international standard eBEACOPP therapy

– ADCETRIS regimen showed less peripheral neuropathy

Seagen Inc. (NASDAQ: SGEN) today announced that the clinical research cooperative German Hodgkin Study Group (GHSG) presented results showing that a phase 3 trial of ADCETRIS^® in combination with chemotherapy – a regimen called BrECADD (brentuximab vedotin [ADCETRIS], etoposide, cyclophosphamide, doxorubicin [Adriamycin], dacarbazine, and dexamethasone) – met its co-primary endpoints of non-inferior efficacy and superior tolerability versus a highly efficacious yet chemotherapy-intense treatment regimen of escalated BEACOPP (bleomycin, etoposide, doxorubicin (Adriamycin), cyclophosphamide, vincristine, procarbazine, and prednisone), which is an international standard of care in the frontline advanced classical Hodgkin lymphoma (cHL) setting and commonly used in Europe. Both study arms used PET scans to guide treatment decisions. The data results of the HD21 study were presented in a late-breaking session at the 17^th International Conference on Malignant Lymphoma (ICML) in Lugano, Switzerland on June 17.

An interim analysis at 40 months showed an unprecedented 94.9% 3-year progression-free survival (PFS) (99% CI: 92.8, 97.1) for patients treated with the ADCETRIS combination of BrECADD versus 92.3% for eBEACOPP (99% CI: 89.7, 94.9). 12-month post-treatment safety data were consistent with previously presented HD21 data results at the American Society of Hematology 2022 Annual Meeting.

ADCETRIS + AVD chemotherapy (Adriamycin, vinblastine, dacarbazine) is a U.S. standard of care in advanced-stage cHL and is the only targeted therapy inclusive regimen that has a proven statistically significant overall survival benefit at 6-years of follow-up compared to ABVD, reducing risk of death by 41% for these patients.ⁱ,ⁱⁱ ADCETRIS is approved for seven indications in the U.S. and six indications in Europe, where Takeda has commercialization rights.

“Our mission in Hodgkin lymphoma is to cure patients with a first-line treatment that reduces the risk of cancer returning as much as possible so patients can go on with their lives,” said Professor Dr. med. Peter Borchmann, Assistant Medical Director, Department of Hematology and Oncology at the University Hospital of Cologne, Germany and Head of the Lymphoma Program, Head of the German Hodgkin Study Group and Trial Chairman of the HD21 study. “The mature results of this study demonstrate 3-year efficacy never previously observed in a phase 3 trial in advanced cHL and suggest that the BrECADD regimen may be the most effective therapy regimen currently available in advanced cHL.”

“We are enthusiastic about these strong and durable efficacy outcomes and tolerability findings of an ADCETRIS based chemotherapy regimen compared to an international standard chemotherapy. We are evaluating these results to determine next steps,” said Roger Dansey, President of Research and Development and Chief Medical Officer at Seagen.

Results from the GHSG’s HD21 Trial

Among 1,482 patients at median follow up of 40 months, an intent-to-treat analysis showed:

• 3-year PFS was 94.9% for BrECADD vs. 92.3% for eBEACOPP (HR=0.63 [99% CI: 0.37, 1.07])
• 1-year PFS was 97.5% for BrECADD (99% CI: 96, 99)
• 3-year overall survival was 98.5% in both treatment arms

12-month post-treatment safety information was available for 95 percent of patients (n=1,395), which showed the rate of grade ≥2 peripheral neuropathy was lower with BrECADD (1.9%) vs. eBEACOPP (2.7%) with most patients having no or low (grade 1) peripheral neuropathy (98.1% for BrECADD vs. 97.3% for eBEACOPP).

Preservation of fertility potential was indicated by measurement of follicle-stimulating hormone (FSH) and was available for 597 patients. Preservation of fertility potential was numerically favorable for the BrECADD arm vs. eBEACOPP. Mean FSH levels were 29.4 and 31.8 after 4 and 6 cycles, respectively for eBEACOPP, and 18.3 and 20.5 after 4 and 6 cycles, respectively, for BrECADD. Persistently elevated FSH is associated with impaired gonadal function. Additional analysis is required to understand the significance of these findings.

Please see Important Safety Information, including a BOXED WARNING for progressive multifocal leukoencephalopathy (PML), for ADCETRIS below.

About the HD21 Study

The GHSG’s phase 3 HD21 trial in advanced cHL enrolled 1,500 patients from 9 countries between July 2016 and August 2020. The median age was 34 years old (range 18-61), and 47 percent were considered high-risk with an international prognostic index ≥3. 59% of patients received four cycles of therapy and 41% received six cycles of therapy. Patients were randomized in a 1:1 ratio to PET2-guided 4-6 cycles of either BrECADD or eBEACOPP. PET2 and PFS events were assessed by blinded panel review. Non-inferiority of the primary efficacy endpoint PFS was defined as absolute difference <6% at five years corresponding to an HR of BrECADD vs eBEACOPP <1.69. The study was funded by Takeda.

About Hodgkin Lymphoma

Lymphoma is a general term for a group of cancers that originate in the lymphatic system affecting a type of white blood cell called lymphocytes. There are two major categories of lymphoma: Hodgkin lymphoma and non-Hodgkin lymphoma. Hodgkin lymphoma is distinguished by the presence of Reed-Sternberg cells that usually have a protein called CD30 on their surface. Approximately 8,830 cases of classical Hodgkin lymphoma will be diagnosed in the United States during 2023 and 900 people will die from the disease.ⁱⁱⁱ According to the International Agency for Research on Cancer in 2020, over 83,000 people worldwide were diagnosed with Hodgkin lymphoma and approximately 23,000 people died from this cancer.^iv

About The German Hodgkin Study Group

For over 30 years, the German Hodgkin Study Group (GHSG) has been committed to optimizing diagnostics, therapy and follow-up care in Hodgkin lymphoma. The GHSG’s Trial Coordination Center belongs to the Department of Internal Medicine at the University of Cologne. It recruits patients from across Europe, and over 15,000 patients have participated in its clinical trials. With the results of its large-scale controlled, prospective and randomized trials for all stages of Hodgkin lymphoma, the GHSG has contributed decisively to the great progress in Hodgkin lymphoma therapy over the years. The GHSG’s latest trials aim to reduce adverse effects of therapy while maintaining cure rates.

About ADCETRIS

ADCETRIS is an antibody-drug conjugate (ADC) comprised of a CD30-directed monoclonal antibody attached by a protease-cleavable linker to a microtubule disrupting agent, monomethyl auristatin E (MMAE), utilizing Seagen's 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-positive tumor cells.

ADCETRIS is approved in seven indications in the U.S.:

• Adult patients with previously untreated Stage III/IV cHL in combination with doxorubicin, vinblastine, and dacarbazine (2018)
• Pediatric patients 2 years and older with previously untreated high risk cHL in combination with doxorubicin, vincristine, etoposide, prednisone and cyclophosphamide (2022)
• Adult patients with cHL at high risk of relapse or progression as post-autologous hematopoietic stem cell transplantation (auto-HSCT) consolidation (2015)
• Adult patients with cHL after failure of auto-HSCT or after failure of at least two prior multi-agent chemotherapy regimens in patients who are not auto-HSCT candidates (2011)
• Adult patients with 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 (2018)
• Adult patients with sALCL after failure of at least one prior multi-agent chemotherapy regimen. (2011)
• Adult patients with primary cutaneous anaplastic large cell lymphoma (pcALCL) or CD30-expressing mycosis fungoides (MF) after prior systemic therapy (2017)

ADCETRIS has marketing authorization in more than 70 countries for relapsed or refractory Hodgkin lymphoma and systemic anaplastic large cell lymphoma. ADCETRIS received conditional marketing authorization from the European Commission in October 2012. Its approved indications in Europe are for:

• Adult patients with previously untreated CD30-positive Stage IV Hodgkin lymphoma in combination with AVD
• Adult patients with CD30-positive Hodgkin lymphoma at increased risk of relapse or progression following ASCT.
• 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.
• Adult patients with relapsed or refractory sALCL
• Adult patients with previously untreated sALCL in combination with CHP
• Adult patients with CD30-positive cutaneous T-cell lymphoma (CTCL) after at least one prior systemic therapy

Seagen and Takeda jointly develop ADCETRIS. Under the terms of the collaboration agreement, Seagen has U.S. and Canadian commercialization rights, and Takeda has rights to commercialize ADCETRIS in the rest of the world. Seagen 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.

ADCETRIS^® (brentuximab vedotin) for injection U.S. Important Safety Information

BOXED WARNING

PROGRESSIVE MULTIFOCAL LEUKOENCEPHALOPATHY (PML): JC virus infection resulting in PML, and death can occur in ADCETRIS-treated patients.

CONTRAINDICATION

Contraindicated with concomitant 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. Patients experiencing new or worsening PN may require a delay, change in dose, or discontinuation of ADCETRIS.

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.

Administer G-CSF primary prophylaxis beginning with Cycle 1 for adult patients who receive ADCETRIS in combination with chemotherapy for previously untreated Stage III/IV cHL or previously untreated PTCL, and pediatric patients who receive ADCETRIS in combination with chemotherapy for previously untreated high risk cHL.

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 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 infections.

Tumor lysis syndrome: Patients with rapidly proliferating tumor and high tumor burden may be at increased risk. Monitor closely and take appropriate measures.

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. 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. 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 have been reported in ADCETRIS-treated patients. First onset of symptoms occurred at various times from initiation of ADCETRIS, 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 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 pre-existing GI involvement may increase the risk of perforation. In the event of new or worsening GI symptoms, including severe abdominal pain, perform a prompt diagnostic evaluation and treat appropriately.

Hyperglycemia: Serious cases, such as new-onset hyperglycemia, exacerbation of pre-existing diabetes mellitus, and ketoacidosis (including fatal outcomes) have been reported with ADCETRIS. Hyperglycemia occurred more frequently in patients with high body mass index or diabetes. Monitor serum glucose and if hyperglycemia develops, administer anti-hyperglycemic medications as clinically indicated.

Embryo-fetal toxicity: Based on the mechanism of action and animal studies, ADCETRIS can cause fetal harm. Advise females of reproductive potential of this potential risk, and to use effective contraception during ADCETRIS treatment and for 2 months after the last dose of ADCETRIS. Advise male patients with female partners of reproductive potential to use effective contraception during ADCETRIS treatment and for 4 months after the last dose of ADCETRIS.

ADVERSE REACTIONS

The most common adverse reactions (≥20% in any study) are peripheral neuropathy, fatigue, nausea, diarrhea, neutropenia, upper respiratory tract infection, pyrexia, constipation, vomiting, alopecia, decreased weight, abdominal pain, anemia, stomatitis, lymphopenia, mucositis, thrombocytopenia, and febrile neutropenia.

DRUG INTERACTIONS

Concomitant use of strong CYP3A4 inhibitors has the potential to affect the exposure to monomethyl auristatin E (MMAE). Closely monitor adverse reactions.

USE IN SPECIAL POPULATIONS

Lactation: Breastfeeding is not recommended during ADCETRIS treatment.

Please see the full Prescribing Information, including BOXED WARNING, for ADCETRIS here.

About Seagen

Founded 25 years ago, Seagen Inc. is a global biotechnology company that discovers, develops, manufactures and commercializes targeted cancer therapeutics, with antibody-drug conjugates (ADCs) at our core. Our colleagues work together with urgency to improve and extend the lives of people living with cancer. An ADC technology trailblazer, approximately one-third of FDA-approved and marketed ADCs use Seagen technology. Seagen is headquartered in Bothell, Washington and has locations in California, Canada, Switzerland and across Europe. For additional information, visit seagen.com and follow us on Twitter and LinkedIn.

Forward-Looking Statements

Certain statements made in this press release are forward looking, such as those, among others, relating to the therapeutic potential of ADCETRIS, its safety, efficacy and therapeutic uses. 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 without limitation the risk of delays, setbacks or failures in product development activities, even after encouraging results in earlier-stage trials, for a variety of reasons, including without limitation the difficulty and uncertainty of pharmaceutical product development, the possibility that clinical results may not support continued development or regulatory approvals, the risk of adverse events or safety signals, and the possibility of adverse regulatory actions. More information about the risks and uncertainties faced by Seagen is contained under the caption “Risk Factors” included in Seagen’s Quarterly Report on Form 10-Q for the quarter ended March 31, 2023, and Seagen’s subsequent reports, filed with the Securities and Exchange Commission. Seagen 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 applicable law.

ⁱ https://www.nccn.org/guidelines/guidelines-detail?category=1&id=1439

ⁱⁱ https://www.nejm.org/doi/full/10.1056/NEJMoa2206125

ⁱⁱⁱ https://www.cancer.org/cancer/hodgkin-lymphoma/about/key-statistics.html

^iv https://gco.iarc.fr/today/data/factsheets/cancers/33-Hodgkin-lymphoma-fact-sheet.pdf

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