Safety and Tolerability of Bintrafusp Alfa, a Bifunctional Fusion Protein Targeting TGFβ and PD-L1, in Asian Patients with Pretreated Recurrent or Refractory Gastric Cancer

Abstract Purpose: Patients with advanced gastric/gastroesophageal junction cancer (GC/GEJC) have limited treatment options after first-line therapy. Bintrafusp alfa is a first-in-class bifunctional fusion protein composed of the extracellular domain of the TGFβRII receptor (a TGFβ “trap”) fused to a human IgG1 antibody against programmed death ligand 1 (PD-L1), potentially offering a new treatment approach for these patients. We report results for bintrafusp alfa in GC/GEJC. Patients and Methods: Asian patients with recurrent GC/GEJC for whom standard therapy does not exist or for whom standard therapy has failed enrolled in this expansion cohort of an ongoing phase I trial and received bintrafusp alfa 1,200 mg once every 2 weeks until disease progression, unacceptable toxicity, or withdrawal. The primary objective was to assess safety/tolerability. Results: By July 23, 2018, 31 heavily pretreated patients received bintrafusp alfa for a median of 10.1 weeks; 3 patients remained on treatment. Six patients (19%) experienced grade 3 treatment-related adverse events (AE); no grade 4 events occurred. One on-treatment death occurred (sudden death); rupture of a preexisting thoracic aortic aneurysm was the suspected cause. Ten patients (32%) had immune-related AEs. The confirmed objective response rate per independent review committee was 16%; disease control rate was 26%. Median duration of response was 8.7 months (range, 2.4–12.4+). Responses occurred irrespective of PD-L1 expression or microsatellite instability status and appeared to correlate with high tumor TGFB1 levels. Conclusions: In this first evaluation in Asian patients with heavily pretreated advanced GC/GEJC, bintrafusp alfa demonstrated a manageable safety profile and clinical activity.