Seattle Genetics’s trial of tucatinib in HER2-positive breast cancer meets primary and secondary endpoints

Seattle Genetics’s trial of tucatinib in HER2-positive breast cancer has met primary and secondary endpoints, showing that the addition of tucatinib was superior to trastuzumab and capecitabine alone, and the company is planning NDA Submission to U.S. FDA for first quarter of 2020.

BOTHELL, Wash.–(BUSINESS WIRE)–Seattle Genetics, Inc. (Nasdaq:SGEN) today announced positive topline results from the HER2CLIMB trial, a randomized, double-blind, placebo-controlled, active comparator pivotal trial evaluating tucatinib. The trial 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), and 47 percent of the patients enrolled in the trial had brain metastases at the time of enrollment. Tucatinib is an oral, small molecule tyrosine kinase inhibitor (TKI) that is highly selective for HER2.

The trial met the primary endpoint of progression-free survival (PFS), showing 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 also 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 trastuzumab and capecitabine alone. 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 those who received trastuzumab and capecitabine alone (HR=0.48 (95% CI: 0.34, 0.69); p<0.00001).

Tucatinib in combination with trastuzumab and capecitabine was generally well tolerated with a manageable safety profile. The most frequent adverse events in the tucatinib arm included diarrhea, palmar-plantar erythrodysaesthesia syndrome (PPE), nausea, fatigue, and vomiting. Grade 3 or greater adverse events in the tucatinib arm compared to the control arm included diarrhea (12.9 vs. 8.6 percent), increased aspartate aminotransferase (AST) (4.5 vs. 0.5 percent), increased alanine aminotransferase (ALT) (5.4 vs. 0.5 percent) and increased bilirubin (0.7 vs. 2.5 percent). There was no requirement for prophylactic antidiarrheals. Adverse events leading to discontinuations were infrequent in both the tucatinib arm and the control arm (5.7 and 3.0 percent). Additional results are scheduled to be presented on December 11 at the 2019 San Antonio Breast Cancer Symposium.

“There is significant unmet medical need following treatment with trastuzumab, pertuzumab and T-DM1 in patients with metastatic HER2-positive breast cancer,” said Roger Dansey, M.D., Chief Medical Officer at Seattle Genetics. “The addition of tucatinib to the commonly used doublet of trastuzumab and capecitabine represents a potential significant clinical advance for patients with metastatic HER2-positive breast cancer, importantly, including those with brain metastases. Based on these findings, we plan to unblind the trial and offer tucatinib to patients on the control arm. We also plan to submit a New Drug Application (NDA) to the FDA in the first quarter of 2020, with the goal of bringing a much-needed new medicine to patients.”