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 PD-L1 positive as defined by a combined positive score (CPS), i.e. CPS ≥ 1 by approved, commercial diagnostic assay * Tumor must be HER2 negative as determined by a CLIA-approved laboratory 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