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.