Study of Suratadenoturev (OBP-301) in Combination With Pembrolizumab in Esophagogastric Adenocarcinoma

This is a phase II study of suratadenoturev (OBP-301) with pembrolizumab in advanced or metastatic gastric, gastroesophageal junction, or esophageal adenocarcinoma that has progressed on at least 1 line of prior therapy for advanced disease. Patients must have received prior immunotherapy (anti PD-1 therapy). This study will examine the addition of OBP-301 with pembrolizumab patients who are refractory to first line immunotherapy.

Patients will undergo intra-tumoral injection of OBP-301 followed 2-4 days later by the administration of pembrolizumab. The OBP-301 injection will then be repeated every two weeks for 4 planned treatments, and up to one additional optional treatment. Pembrolizumab will be administered every 6 weeks until disease progression.

The primary endpoint is objective response rate, with the target response rate of 20%, to examine the hypothesis that OBP-301 can overcome checkpoint resistance. The expected response to continuing anti-PD-1 therapy in this patient population would anticipated to be \<5%. As a key secondary endpoint, the investigators will also examine duration of response and progression free survival. In a previous trial of OBP-301 and pembrolizumab in the third line setting, two patients who had a partial response are now off therapy and without evidence of disease, with a duration of response 33+ months and 20+ months. The third patient with a partial response has been on therapy for 15+ months.

This trial utilizes a Simon's two-stage Minimax design. In the first stage of the trial, 13 patients will be accrued. If there are 0 responses in these 13 patients, the study will be stopped. Otherwise, 14 additional patients will be accrued for a total of 27 patients.