On December 18, 2019 Seattle Genetics, Inc. (Nasdaq:SGEN) reported that the U.S. Food and Drug Administration (FDA) has granted Breakthrough Therapy designation to tucatinib, in combination with trastuzumab and capecitabine, for 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 (Press release, Seattle Genetics, DEC 18, 2019, View Source [SID1234552476]). The positive topline results of the pivotal HER2CLIMB clinical trial were announced in October 2019, and additional data were presented at the 2019 San Antonio Breast Cancer Symposium (SABCS) on December 11, 2019 and were simultaneously published in the New England Journal of Medicine (NEJM). Tucatinib is an oral, small molecule tyrosine kinase inhibitor (TKI) that is highly selective for HER2.
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The FDA’s Breakthrough Therapy process is intended to expedite the development and review of promising drug candidates intended for serious or life-threatening conditions. Designation is based upon preliminary clinical evidence of the potential for substantial improvement over existing therapies on one or more clinically significant endpoints.
"The addition of tucatinib to the commonly used combination of trastuzumab and capecitabine demonstrated superior activity compared to trastuzumab and capecitabine alone in patients with unresectable locally advanced or metastatic HER2-positive breast cancer, including those with and without brain metastases," said Roger Dansey, M.D., Chief Medical Officer at Seattle Genetics. "The decision by the FDA to grant Breakthrough Therapy designation to tucatinib recognizes the urgent need for new medicines that can impact the lives of those with HER2-positive metastatic breast cancer. We intend to submit a New Drug Application to the FDA and an MAA to the EMA by the first quarter 2020, with the goal of making tucatinib available to patients in this setting as soon as possible."
This Breakthrough Therapy designation was 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 ado-trastuzumab emtansine (T-DM1). 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.
Data presented at SABCS and published in NEJM include the primary endpoint of progression-free survival (PFS) as assessed by blinded independent central review (BICR) in the first 480 patients enrolled in the trial. The primary endpoint of PFS showed that the addition of tucatinib was superior to trastuzumab and capecitabine alone, with a 46 percent reduction in the risk of disease progression or death (hazard ratio (HR)=0.54 (95% Confidence Interval (CI): 0.42, 0.71); p<0.00001). The trial met the two key secondary endpoints at interim analysis. The tucatinib arm demonstrated an improvement in overall survival, with a 34 percent reduction in the risk of death (HR=0.66 [95% CI: 0.50, 0.88]; p=0.0048), compared to the control arm. For patients with brain metastases at baseline, the tucatinib arm also demonstrated superior PFS, with a 52 percent reduction in the risk of disease progression or death, compared to the control arm (HR=0.48 [95% CI: 0.34, 0.69]; p<0.00001).
Tucatinib in combination with trastuzumab and capecitabine was generally well tolerated. The most common adverse events occurring in more than 20 percent of patients in the tucatinib arm vs. the control arm included diarrhea, palmar-plantar erythrodysaesthesia syndrome (PPE), nausea, fatigue, and vomiting. Discontinuation of tucatinib and placebo due to adverse events was 5.7 percent in the tucatinib arm and 3.0 percent in the control arm. Greater than or equal to Grade 3 diarrhea was seen in 12.9 percent of the patients in the tucatinib arm vs. 8.6 percent in the control arm. Antidiarrheal prophylaxis was not required per protocol. Antidiarrheals were used in less than half of all cycles where diarrhea was reported. In both treatment arms, when used, the duration of antidiarrheal treatment was short (median of 3 days/cycle). Greater than or equal to Grade 3 aspartate aminotransferase (AST) was seen in 4.5 percent of the patients in the tucatinib arm vs. 0.5 percent in the control arm, and alanine aminotransferase (ALT) elevation in 5.4 percent vs. 0.5 percent, respectively. Discontinuations due to liver transaminase elevations were infrequent in both arms (ALT: 1.0 vs. 0.5 percent; AST: 0.7 vs. 0.5 percent).
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 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 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. Safety data were evaluated throughout the study.
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 progression-free survival per RECIST criteria. Secondary endpoints include overall survival, objective response rate and duration of response. The trial is being conducted in North America and is expected to enroll approximately 460 patients. More information about the phase 3 trial, including enrolling centers, is available at 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 objective response rate by RECIST criteria. Progression-free survival, 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) (Free ESMO Whitepaper) 2019 Congress. Enrollment is ongoing. More information about the MOUNTAINEER trial, including enrolling centers, is available at www.clinicaltrials.gov.