The investigational bispecific T-cell engager (BiTE) PRS-343 was well tolerated and demonstrated anti-tumor activity in previously treated patients with human epidermal growth factor receptor 2-positive (HER2+) tumors, according to research presented at the Society for Immunotherapy of Cancer Annual Meeting.
The ongoing open-label, multicenter, first-in-human, phase I, dose-escalation study included 53 patients (median age, 61 years; 59% received more than three previous lines of therapy) with the following HER2+ metastatic tumors: gastric/esophagogastric junction cancer (n=19), breast cancer (n=14), gynecologic cancer (n=6), colorectal cancer (n=5), biliary tract cancer (n=4), urothelial cancer (n=2), melanoma (n=1), pancreatic cancer (n=1), and salivary duct cancer (n=1).
Demonstration of single-agent anti-tumor activity
Patients received PRS-343 at intravenous doses ranging from 0.0005 mg/kg to 8 mg/kg every three weeks. Patients who received the 8 mg/kg dose were treated every two weeks. Researchers determined the low end of the active dose range to be 2.5 mg/kg.
Nineteen patients were evaluable at data cutoff. There was a disease control rate of 58%, with 11% of patients experiencing confirmed partial response.
There were no grade 3/4 treatment-related adverse events (AEs). The most common AEs were fatigue (9%), chills (6%), and diarrhea (5%), none of which were deemed dose-limiting toxicities.