Early Access Program for Zolbetuximab

Inclusion Criteria: * Patient has histologically confirmed diagnosis of gastric or gastroesophageal junction adenocarcinoma. * Patient has confirmed locally advanced, unresectable or metastatic gastric or GEJ adenocarcinoma. * Patient whose tumor expresses claudin18.2 (CLDN18.2) in ≥ 75% of tumor cells demonstrating moderate to strong membranous CLDN18 staining as determined by local or central immunohistochemistry (IHC) testing. * Patient has a Human epidermal growth factor receptor 2 (HER2-negative) tumor by local testing on a gastric or GEJ tumor specimen. * Patient has Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1. * Patient must meet all of the following criteria based on the locally analyzed laboratory tests collected. * Hemoglobin (Hgb) ≥ 9 g/dL. Patients requiring transfusions are eligible if they have post-transfusion Hgb ≥ 9 g/dL. * Absolute neutrophil count (ANC) ≥ 1.5 × 109/L * Platelets ≥ 100 × 109/L * Albumin ≥ 2.5 g/dL * Total bilirubin (TBL) ≤ 1.5 × ULN without liver metastases (or \< 3.0 × ULN if liver metastases are present) * Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 2.5 × upper limit of normal (ULN) without liver metastases (or ≤ 5 × ULN if liver metastases are present) * Estimated creatinine clearance ≥ 30 mL/min * Prothrombin time/international normalized ratio (PT/INR) and partial thromboplastin time ≤ 1.5 × ULN (except for patients receiving anticoagulation therapy) * Female patient is not pregnant and at least 1 of the following conditions apply: * Not a woman of child bearing potential (WOCBP) * WOCBP who agrees to follow the contraceptive guidance from the time of informed consent through at least 9 months after the final administration of oxaliplatin and 6 months after final administration of other interventions. * Female patient must agree not to breastfeed starting at screening and throughout the EAP period and for 6 months after final intervention administration. * Female patient must not donate ova starting at first administration of treatment and throughout the EAP period and for 9 months after the final administration of oxaliplatin and 6 months after final administration of other interventions. * Male patient with female partner(s) of childbearing potential (including breastfeeding partner) must agree to use contraception throughout the treatment period and for 6 months after final treatment administration. * Male patient must not donate sperm during the treatment period and for 6 months after final treatment administration. * Male patient with pregnant partner(s) must agree to remain abstinent or use a condom for the duration of the pregnancy throughout the EAP period and for 6 months after final treatment administration. Exclusion Criteria: * Patient has previously received treatment in a clinical trial of zolbetuximab, or a clinical trial that included zolbetuximab as 1 of the treatment options, even if the patient was not given zolbetuximab. * Patient is a candidate for an ongoing clinical trial of zolbetuximab. * Patient has received any investigational therapy within 28 days or 5 half-lives prior to screening. * Patient has a known or suspected hypersensitivity to zolbetuximab, other monoclonal antibodies or any components of the formulation used. * Patient has received prior systemic chemotherapy for locally advanced unresectable or metastatic gastric or GEJ adenocarcinoma. However, patient may have received either neo-adjuvant or adjuvant chemotherapy, immunotherapy or other systemic anticancer therapies as long as it was completed at least 6 months prior to participation. * Patient has received radiotherapy for locally advanced unresectable or metastatic gastric or GEJ adenocarcinoma ≤ 14 days prior to program registration and has not recovered from any related toxicity. * Patient receiving treatment with herbal medications that have known antitumor activity. * Patient has received systemic immunosuppressive therapy, including systemic corticosteroids within 14 days prior to registration. Patients using a physiologic replacement dose of hydrocortisone or its equivalent (defined as up to 30 mg/day of hydrocortisone or up to 10 mg/day of prednisone), receiving a single dose of systemic corticosteroids or receiving systemic corticosteroids as premedication for radiologic imaging contrast use are allowed. * Patient has a prior severe allergic reaction, known (immediate or delayed) or suspected hypersensitivity, intolerance or contraindication to zolbetuximab, mFOLFOX6, CAPOX, other monoclonal antibodies or any components of the formulations used. * Patient has known dihydropyrimidine dehydrogenase (DPD) deficiency. (NOTE: Screening for DPD deficiency should be conducted per local requirements.) * Patient has a complete gastric outlet syndrome or a partial gastric outlet syndrome with persistent/recurrent vomiting. * Patient has significant gastric bleeding and/or untreated gastric ulcers that would exclude the patient from participation. * Patient has any other condition, which makes the patient unsuitable to receive or tolerate zolbetuximab.