Business Wire | Dec 8, 2020 08:00AM EST

Seagen Highlights TUKYSA(r) (tucatinib) Data in Breast Cancer at Virtual 2020 San Antonio Breast Cancer Symposium

Dec. 08, 2020

BOTHELL, Wash.--(BUSINESS WIRE)--Dec. 08, 2020--Seagen Inc. (Nasdaq:SGEN) today announced the presentation of new data from TUKYSA (tucatinib), its HER2-positive metastatic breast cancer therapy, at the San Antonio Breast Cancer Symposium (SABCS) Virtual Symposium, taking place December 8-11, 2020. Nine abstracts - including two spotlight posters - highlight the company's commitment to addressing unmet needs in breast cancer.

"Following this year's FDA approval of TUKYSA, we continue to broadly study if more patients may benefit from this important medicine," said Roger Dansey, M.D., Chief Medical Officer at Seagen. "Data presented at the meeting from the HER2CLIMB trial demonstrate TUKYSA's efficacy regardless of patients' hormone receptor status, while other clinical and preclinical findings provide new insights about TUKYSA's potential to help patients living with HER2-positive metastatic breast cancer."

Highlights for key data presentations at the meeting include:

Efficacy Outcomes by Hormone Receptor Status from HER2CLIMB Trial

Outcomes for TUKYSA(r) (tucatinib) in combination with trastuzumab and capecitabine in patients with HER2-positive metastatic breast cancer from the pivotal HER2CLIMB trial by hormone receptor (HR) status will be featured in a spotlight poster (Abstract #PD3-08). Results will be presented by Erika P. Hamilton, M.D., Director, Breast Cancer and Gynecologic Cancer Research Program at the Sarah Cannon Research Institute.

As previously reported, the addition of TUKYSA to trastuzumab and capecitabine resulted in clinically meaningful improvements in overall survival (OS), progression-free survival (PFS) and objective response rate (ORR) compared to the addition of placebo. The new exploratory analyses presented at SABCS demonstrated that the PFS, OS and ORR improvements with TUKYSA were observed consistently across hormone receptor status subgroups, including in patients with brain metastases.

SABCS 2020 Data Presentations for Seagen Medicines and Pipeline Agents:

Below are presentation details related to TUKYSA and the investigational agent ladiratuzumab vedotin at SABCS. Published abstracts can be found here. Poster presentations will be available on December 9, 2020.

Abstract Title Abstract Presentation Presenter No. Type / Date

Tucatinib versus placebo incombination with trastuzumab and Spotlight Postercapecitabine for patients with Discussion 3 -locally advanced unresectable or #PD3-08 Wednesday, Dec. 9 E. HamiltonHER2-positive metastatic breast from 6:45 - 7:45cancer (HER2CLIMB): outcomes by p.m. CThormone receptor status

Impact of tucatinib on Spotlight Posterhealth-related quality of life in Discussion 13 -patients with HER2+ metastatic #PD13-04 Friday, Dec. 11 A. Wardleybreast cancer with stable and active from 1 - 2:15 p.m.brain metastases CT

Tucatinib favourably modulates theimmune microenvironment and Poster Session 10synergises with anti-PD1 therapy in #PS10-04 / Wednesday, Dec. R. Lia trastuzumab resistant HER2+ murine 9 at 8 a.m. CTmodel

Tucatinib potentiates the activity Poster Session 10of the antibody-drug conjugate T-DM1 #PS10-08 / Wednesday, Dec. A. Kulukianin preclinical models of 9 at 8 a.m. CTHER2-positive breast cancer

Real world treatment patterns andhealthcare resource utilization Poster Session 14among HER2+ metastatic breast cancer #PS14-15 / Wednesday, Dec. C. Ikepatients with and without brain 9 at 8 a.m. CTmetastases: a retrospective cohortstudy

Interim safety and efficacy analysisof phase IB/II clinical trial of Poster Session 10tucatinib, palbociclib and letrozole #PS10-03 / Wednesday, Dec. E.in patients with hormone receptor 9 at 8 a.m. CT Shagisultanovaand HER2-positive metastatic breastcancer

Trials-in-Progress

HER2CLIMB-02: A randomized, Ongoing Trialsdouble-blind, phase 3 study of # Posters /tucatinib or placebo with T-DM1 for OT-28-01 Wednesday, Dec. 9 S. Hurvitzunresectable locally-advanced or at 8 a.m. CTmetastatic HER2+ breast cancer

SGNLVA-001: a phase 1 open-label Ongoing Trialsdose escalation and expansion study # Posters / H.C. Beckwithof SGN-LIV1A administered weekly in OT-03-03 Wednesday, Dec. 9breast cancer at 8 a.m. CT

About TUKYSA (tucatinib)

TUKYSA is an oral medicine that is a tyrosine kinase inhibitor of the HER2 protein. In vitro (in lab studies), TUKYSA inhibited phosphorylation of HER2 and HER3, resulting in inhibition of downstream MAPK and AKT signaling and cell growth (proliferation), and showed anti-tumor activity in HER2-expressing tumor cells. In vivo (in living organisms), TUKYSA inhibited the growth of HER2-expressing tumors. The combination of TUKYSA and the anti-HER2 antibody trastuzumab showed increased anti-tumor activity in vitro and in vivo compared to either medicine alone. In the U.S., TUKYSA is approved in combination with trastuzumab and capecitabine for adult patients with advanced unresectable or metastatic HER2-positive breast cancer, including patients with brain metastases (disease that has spread to the brain), who have received one or more prior anti-HER2-based regimens in the metastatic setting. TUKYSA is approved in the U.S., Switzerland, Canada, Singapore and Australia and is under review in the European Union. As part of a strategic collaboration announced in September 2020 with Merck, known as MSD outside the United States and Canada, Merck has exclusive rights to commercialize TUKYSA in Asia, the Middle East and Latin America and other regions outside of the U.S., Canada and Europe.

U.S. Important Safety Information

Warnings and Precautions

* Diarrhea - TUKYSA can cause severe diarrhea including dehydration, hypotension, acute kidney injury, and death. In HER2CLIMB, 81% of patients who received TUKYSA experienced diarrhea, including 12% with Grade 3 diarrhea and 0.5% with Grade 4 diarrhea. Both patients who developed Grade 4 diarrhea subsequently died, with diarrhea as a contributor to death. The median time to onset of the first episode of diarrhea was 12 days and the median time to resolution was 8 days. Diarrhea led to dose reductions of TUKYSA in 6% of patients and discontinuation of TUKYSA in 1% of patients. Prophylactic use of antidiarrheal treatment was not required on HER2CLIMB. If diarrhea occurs, administer antidiarrheal treatment as clinically indicated. Perform diagnostic tests as clinically indicated to exclude other causes of diarrhea. Based on the severity of the diarrhea, interrupt dose, then dose reduce or permanently discontinue TUKYSA. * Hepatotoxicity - TUKYSA can cause severe hepatotoxicity. In HER2CLIMB, 8% of patients who received TUKYSA had an ALT increase >5 x ULN, 6% had an AST increase >5 x ULN, and 1.5% had a bilirubin increase >3 x ULN (Grade 3). Hepatotoxicity led to dose reduction of TUKYSA in 8% of patients and discontinuation of TUKYSA in 1.5% of patients. Monitor ALT, AST, and bilirubin prior to starting TUKYSA, every 3 weeks during treatment, and as clinically indicated. Based on the severity of hepatotoxicity, interrupt dose, then dose reduce or permanently discontinue TUKYSA.

* Embryo-Fetal Toxicity - TUKYSA can cause fetal harm. Advise pregnant women and females of reproductive potential risk to a fetus. Advise females of reproductive potential, and male patients with female partners of reproductive potential, to use effective contraception during TUKYSA treatment and for at least 1 week after the last dose.

Adverse Reactions

Serious adverse reactions occurred in 26% of patients who received TUKYSA. Serious adverse reactions in 2% of patients who received TUKYSA were diarrhea (4%), vomiting (2.5%), nausea (2%), abdominal pain (2%), and seizure (2%). Fatal adverse reactions occurred in 2% of patients who received TUKYSA including sudden death, sepsis, dehydration, and cardiogenic shock.

Adverse reactions led to treatment discontinuation in 6% of patients who received TUKYSA; those occurring in 1% of patients were hepatotoxicity (1.5%) and diarrhea (1%). Adverse reactions led to dose reduction in 21% of patients who received TUKYSA; those occurring in 2% of patients were hepatotoxicity (8%) and diarrhea (6%).

The most common adverse reactions in patients who received TUKYSA (20%) were diarrhea, palmar-plantar erythrodysesthesia, nausea, fatigue, hepatotoxicity, vomiting, stomatitis, decreased appetite, abdominal pain, headache, anemia, and rash.

Lab Abnormalities

In HER2CLIMB, Grade 3 laboratory abnormalities reported in 5% of patients who received TUKYSA were: decreased phosphate, increased ALT, decreased potassium, and increased AST. The mean increase in serum creatinine was 32% within the first 21 days of treatment with TUKYSA. The serum creatinine increases persisted throughout treatment and were reversible upon treatment completion. Consider alternative markers of renal function if persistent elevations in serum creatinine are observed.

Drug Interactions

* Strong CYP3A or Moderate CYP2C8 Inducers: Concomitant use may decrease TUKYSA activity. Avoid concomitant use of TUKYSA. * Strong or Moderate CYP2C8 Inhibitors: Concomitant use of TUKYSA with a strong CYP2C8 inhibitor may increase the risk of TUKYSA toxicity; avoid concomitant use. Increase monitoring for TUKYSA toxicity with moderate CYP2C8 inhibitors. * CYP3A Substrates: Concomitant use may increase the toxicity associated with a CYP3A substrate. Avoid concomitant use of TUKYSA where minimal concentration changes may lead to serious or life-threatening toxicities. If concomitant use is unavoidable, decrease the CYP3A substrate dosage. * P-gp Substrates: Concomitant use may increase the toxicity associated with a P-gp substrate. Consider reducing the dosage of P-gp substrates where minimal concentration changes may lead to serious or life-threatening toxicity.

Use in Specific Populations

* Lactation: Advise women not to breastfeed while taking TUKYSA and for at least 1 week after the last dose. * Renal Impairment: Use of TUKYSA in combination with capecitabine and trastuzumab is not recommended in patients with severe renal impairment (CLcr < 30 mL/min), because capecitabine is contraindicated in patients with severe renal impairment. * Hepatic Impairment: Reduce the dose of TUKYSA for patients with severe (Child-Pugh C) hepatic impairment.

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

About Seagen

Seagen is a global biotechnology company that discovers, develops and commercializes transformative cancer medicines to make a meaningful difference in people's lives. Seagen is headquartered in the Seattle, Washington area, and has locations in California, Canada, Switzerland and the European Union. For more information on the company's marketed products and robust pipeline, visit www.seagen.com and follow @SeagenGlobal on Twitter.

Forward Looking Statements

Certain statements made in this press release are forward looking, such as those, among others, relating to the therapeutic potential of TUKYSA including its efficacy, safety 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 the difficulty and uncertainty of pharmaceutical product development, the risk of adverse events or safety signals, the inability to show sufficient activity in clinical trials 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 the company's Quarterly Report on Form 10-Q for the quarter ended September 30, 2020 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 law.

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CONTACT: Peggy Pinkston (425) 527-4160 ppinkston@seagen.com