<scp>ONO</scp>‐4578 Plus Nivolumab in Unresectable Advanced or Recurrent Gastric or Gastroesophageal Junction Cancer

ONO-4578, an EP4 antagonist, alone and combined with nivolumab, showed acceptable safety profiles and signs of antitumor activity in solid tumors. The expansion part examined the safety, preliminary efficacy, and biomarkers of ONO-4578 plus nivolumab in unresectable advanced or recurrent gastric or gastroesophageal junction (G/GEJ) cancer. Patients were enrolled into three groups: with previous immuno-oncology treatment (IO-treated; n = 30), without IO treatment (IO-naive; n = 30), and with UGT1A1 polymorphism (UGT1A1p; n = 6). Treatment-related adverse events (TRAEs) occurred in 46 patients (grade 3-4 in 17), with no grade 5 events reported. We confirmed the tolerability of the treatment in UGT1A1p. Objective response and disease control rates were 10.0% and 73.3%, respectively, in IO-treated and 16.7% and 40.0%, respectively, in IO-naive. Biomarker analysis indicated immune activation in the tumor microenvironment after the treatment. In conclusion, ONO-4578 plus nivolumab showed a manageable safety profile and antitumor activity in G/GEJ cancer. Trial Registration: Japan Registry of Clinical Trials number: jRCT2080223441; ClinicalTrials.gov identifier: NCT03155061.