Today, we achieved a significant milestone towards our goal of making tucatinib available to patients with locally advanced unresectable or metastatic HER2-positive breast cancer, including those with brain metastases, around the world, said Roger Dansey, M.D., Chief Medical Officer at Seattle Genetics. We look forward to working with the EMA throughout the review process. If approved, tucatinib has the potential to be a clinically meaningful advance for patients in this disease setting.

The MAA is based on data from the pivotal HER2CLIMB clinical trial, which compared tucatinib in combination with trastuzumab and capecitabine to trastuzumab and capecitabine alone in patients with locally advanced unresectable or metastatic HER2-positive breast cancer. Patients had previously received trastuzumab, pertuzumab and T-DM1 (ado-trastuzumab emtansine). Patients had received a median of four prior lines of therapy overall and three in the metastatic setting. Forty-seven percent of the patients enrolled in the trial had brain metastases at the time of enrollment. Results of the pivotal HER2CLIMB trial were presented during an oral presentation at the 2019 San Antonio Breast Cancer Symposium (SABCS) and simultaneously published in the New England Journal of Medicine (NEJM).

The New Drug Application (NDA) for tucatinib was submitted to the U.S. Food and Drug Administration (FDA) on December 23, 2019 under the Real-Time Oncology Review Pilot Program. The review of the tucatinib NDA is also being conducted under Project Orbis, an initiative of the FDA Oncology Center of Excellence. Project Orbis provides a framework for concurrent submission and review of oncology drugs among participating international partners. Tucatinib was recently granted Breakthrough Therapy designation by the FDA in combination with trastuzumab and capecitabine, for the treatment of patients with locally advanced unresectable or metastatic HER2-positive breast cancer, including patients with brain metastases, who have been treated with trastuzumab, pertuzumab, and T-DM1. This designation was based on data from the HER2CLIMB trial.

About HER2CLIMB

HER2CLIMB is a multinational randomized (2:1), double-blind, placebo-controlled, active comparator, pivotal clinical trial comparing tucatinib in combination with trastuzumab and capecitabine compared with trastuzumab and capecitabine alone in patients with locally advanced unresectable or metastatic HER2-positive breast cancer who were previously treated with trastuzumab, pertuzumab and T-DM1. The primary endpoint of the trial was progression-free survival (PFS) per Response Evaluation Criteria in Solid Tumors (RECIST) v1.1 as determined by blinded independent central review (BICR) in the first 480 patients enrolled in the trial. HER2CLIMB enrolled a total of 612 patients to support the analyses of key secondary endpoints, including overall survival, PFS per BICR in patients with brain metastases at baseline and confirmed objective response rate (ORR). Safety data were evaluated throughout the study.

About HER2-Positive Breast Cancer

Patients with HER2-positive breast cancer have tumors with high levels of a protein called human epidermal growth factor receptor 2 (HER2), which promotes the aggressive spread of cancer cells. An estimated 271,270 new cases of invasive breast cancer will be diagnosed in the U.S. in 2019.1 Between 15 and 20 percent of breast cancer cases worldwide are HER2-positive.2 Historically, HER2-positive breast cancer tends to be more aggressive and more likely to recur than HER2-negative breast cancer.2, 3, 4 In patients with metastatic breast cancer, the most common site of first metastasis is in bone, followed by lung, brain, and liver.5, 6 Up to 50 percent of metastatic HER2-positive breast cancer patients develop brain metastases over time.2, 7 Despite recent treatment advances, there is still a significant need for new therapies that can impact metastatic disease, especially brain metastases. There are currently no approved therapies demonstrating progression-free survival or overall survival benefit for the treatment of patients with HER2-positive metastatic breast cancer after progression on T-DM1.8, 9, 10

About Tucatinib

Tucatinib is an investigational, orally bioavailable, potent tyrosine kinase inhibitor that is highly selective for HER2 without significant inhibition of EGFR. Inhibition of EGFR has been associated with significant toxicities, including skin rash and diarrhea. Tucatinib has shown activity as a single agent and in combination with both chemotherapy and other HER2 targeted agents such as trastuzumab.1,2 Studies of tucatinib in these combinations have shown activity both systemically and in brain metastases. HER2 is a growth factor receptor that is overexpressed in multiple cancers, including breast, colorectal and gastric cancers. HER2 mediates cell growth, differentiation and survival. Tucatinib has been granted orphan drug designation by the FDA for the treatment of breast cancer patients with brain metastases.

In addition to HER2CLIMB, tucatinib is being evaluated in a randomized, double-blind, placebo-controlled, multi-center phase 3 trial of tucatinib in combination with T-DM1 compared to T-DM1 alone, in patients with unresectable locally advanced or metastatic HER2-positive breast cancer, including those with brain metastases, who have had prior treatment with a taxane and trastuzumab. The primary endpoint is PFS per RECIST criteria. Secondary endpoints include overall survival, objective response rate and duration of response. This global trial is expected to enroll approximately 460 patients. More information about the phase 3 trial, including enrolling centers, is available at http://www.clinicaltrials.gov.

Tucatinib is also being evaluated in a multi-center, open-label, single-arm phase 2 clinical trial known as MOUNTAINEER, which is evaluating tucatinib in combination with trastuzumab in patients with HER2-positive, RAS wildtype metastatic or unresectable colorectal cancer. The primary endpoint of the trial is ORR by RECIST criteria. PFS, duration of response, overall survival and safety and tolerability of the combination regimen are secondary objectives. Results for 26 patients were evaluated in an analysis and presented at the European Society for Medical Oncology (ESMO) 2019 Congress. Enrollment is ongoing. More information about the MOUNTAINEER trial, including enrolling centers, is available at http://www.clinicaltrials.gov.

About Seattle Genetics

Seattle Genetics, Inc. is a global biotechnology company that discovers, develops and commercializes transformative medicines targeting cancer to make a meaningful difference in peoples lives. ADCETRIS (brentuximab vedotin) and PADCEVTM (enfortumab vedotin-ejfv) use the companys industry-leading antibody-drug conjugate (ADC) technology. ADCETRIS is approved in certain CD30-expressing lymphomas, and PADCEV is approved in certain metastatic urothelial cancers. In addition, investigational agent tucatinib, a small molecule tyrosine kinase inhibitor, is in late-stage development for HER2-positive metastatic breast cancer, and in clinical development for metastatic colorectal cancer. 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 http://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 the therapeutic potential of tucatinib, including its possible efficacy, safety and therapeutic uses; anticipated development activities including ongoing and future clinical trials; and the potential to obtain regulatory approvals of tucatinib in the United States, the European Union and in countries participating in Project Orbis. 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 possibility of disappointing results in ongoing or future clinical trials despite earlier promising clinical results, the possibility that data from the HER2CLIMB trial may not be sufficient to support approval of tucatinib in the United States, the European Union or in other countries participating in Project Orbis or that other adverse regulatory actions could occur. More information about the risks and uncertainties faced by Seattle Genetics is contained under the caption Risk Factors included in the companys Quarterly Report on Form 10-Q for the quarter ended September 30, 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.

References:

1. American Cancer Society, Cancer Facts and Figures 2018-2019.

2. Loibl S, Gianni L (2017). HER2-positive breast cancer. The Lancet 389(10087): 2415-29.

3. Slamon D, Clark G, Wong S, et al. (1987). Human breast cancer: correlation of relapse and survival with amplification of the HER-2/neu oncogene. Science 235(4785): 177-82.

4. American Cancer Society (ACS) (2018). Breast cancer HER2 status. Accessed: December 10, 2018.

5. Kennecke H, Yerushalmi R, Woods R, et al. (2010). Metastatic Behavior of Breast Cancer Subtypes. Journal of Clinical Oncology 28(20): 3271-7.

6. Berman AT, Thukral AD, Hwang W-T, et al. (2013). Incidence and Patterns of Distant Metastases for Patients With Early-Stage Breast Cancer After Breast Conservation Treatment. Clinical Breast Cancer 13(2): 88-94.

7. Duchnowska R, Loibl S, Jassem J (2018). Tyrosine kinase inhibitors for brain metastases in HER2-positive breast cancer. Cancer Treatment Reviews 67: 71-7.

8. Verma S, Miles D, Gianni L, et al. (2012). Trastuzumab Emtansine for HER2-Positive Advanced Breast Cancer. New England Journal of Medicine 367(19): 1783-91.

9. Geyer CE, Forster J, Lindquist D, et al. (2006). Lapatinib plus Capecitabine for HER2-Positive Advanced Breast Cancer. New England Journal of Medicine 355(26): 2733-43.

10. Blackwell KL, Burstein HJ, Storniolo AM, et al. (2012). Overall Survival Benefit With Lapatinib in Combination With Trastuzumab for Patients With Human Epidermal Growth Factor Receptor 2Positive Metastatic Breast Cancer: Final Results From the EGF104900 Study. Journal of Clinical Oncology 30(21): 2585-92.

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