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

Inclusion Criteria: * Histologically or cytologically confirmed advanced or metastatic gastric, gastroesophageal junction, or esophageal adenocarcinoma amenable to intra-tumoral injection (i.e. at least 1 cm in size) * Tumor must be examined forPD-L1 assessment as defined by a Combined Positive Score (CPS), and approved commercial diagnostic assay * If the PD-L1 CPS score is \> 1, patients must have received at least one line of systemic therapy for advanced disease that includes a PD-1 or PD-L1 inhibitor. 1. Patients must have clinical or radiographic disease progression on 1L therapy, or within three months of the last dose of immunotherapy 2. Patients must be eligible for immunotherapy (i.e. have not had a Grade 3 or 4 immunotherapy related gastrointestinal or pulmonary toxicity, or other immune-related adverse event that excludes them from receiving future immunotherapy per PI discretion) * If the PD-L1 CPS score is \< 1, patients must not have received prior anti-PD-1 or PD-L1 therapy and must have received at least one line of systemic therapy for advanced disease. Exclusion Criteria: * Is currently participating and receiving study therapy or has participated in a study of an investigational agent and received study therapy within 3 weeks of study Day 1. * Has an active autoimmune disease that has required systemic treatment in past 2 years except replacement therapy (eg., thyroxine, insulin, or physiologic corticosteroid) * Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy (greater than equivalent of 20 mg/day) or any other form of immunosuppressive therapy within 7 days prior to study Day 1. * Has known active central nervous system metastases and/or carcinomatous meningitis. * Has had prior anti-cancer monoclonal antibody chemotherapy, targeted small molecule therapy, or radiation therapy within 2 weeks prior to study Day 1, who has not recovered from adverse events due to a previously administered agent. * Has a known additional malignancy within 3 years before the first OBP-301 administration that is progressing or requires active treatment, with the exception of prostate cancer controlled with androgen deprivation therapy. * Has received a live vaccine or live-attenuated vaccine within 30 days before the first dose of study intervention. Administration of killed vaccines is allowed. * Is known to have acute or chronic active hepatitis B virus (HBV), hepatitis C virus (HCV) or human immunodeficiency virus (HIV) * Has a history of (non-infectious) pneumonitis/interstitial lung disease that required steroids or has current pneumonitis/interstitial lung disease. * Has an active infection requiring systemic therapy within 2 weeks of Day 1. * Is unable to comply with protocol procedures * Previous severe hypersensitivity (≥ Grade 3) to any monoclonal antibody * Has not adequately recovered from major surgery or has ongoing surgical complications. * Has had an allogenic tissue/solid organ transplant * Has certain uncontrolled illnesses * Is pregnant or breastfeeding or planning to become pregnant or start breast feeding during the study time period * Is expecting to get someone else pregnant during the study time period