A Study of Zolbetuximab (IMAB362) Plus CAPOX Compared With Placebo Plus CAPOX as First-line Treatment of Subjects With Claudin (CLDN) 18.2-positive, HER2-negative, Locally Advanced Unresectable or Metastatic Gastric or Gastroesophageal Junction (GEJ) Adenocarcinoma (GLOW).

This study is looking for adults who have been diagnosed with advanced stomach cancer or cancer where the food pipe joins the stomach (GEJ cancer). For you to join, your cancer must be locally advanced (spread to nearby tissues) or metastatic (spread to other parts of the body), meaning it can't be fully removed by an operation.

Also, a specific test on your cancer tissue must show that your cancer has the 'Claudin 18.2' protein. You might have had some previous standard treatments, but you must not have had chemotherapy specifically for this cancer yet. There are certain health conditions that would prevent you from joining, such as needing medicines that suppress your immune system, having blockages or bleeding in your gut, certain types of uncontrollable cancer (like in the brain or spine), or specific heart conditions or infections.

If you join this study, you will receive one of two possible treatments by chance: either zolbetuximab with chemotherapy, or a placebo (a dummy drug without medicine) with chemotherapy. Neither you nor your doctor will know which treatment you are receiving (this is called 'double-blinded'). The chemotherapy used is called CAPOX, which involves oxaliplatin given through a tube into a vein, and capecitabine, which is taken as tablets.

Treatment is given in cycles. You will receive an infusion of either zolbetuximab or placebo, along with oxaliplatin, every 3 weeks. You will also take capecitabine tablets twice a day for the first 2 weeks of each cycle. You may continue receiving zolbetuximab or placebo until your cancer gets worse, the side effects become too much, or you need a different cancer treatment. CAPOX chemotherapy is typically given for about 6 months (8 cycles). After this, you might continue with capecitabine tablets alone until your cancer worsens or you can't tolerate the treatment.

You will have regular clinic visits throughout your treatment. Doctors will check for any medical problems or side effects, and you'll have health checks. Scans will be done on some visits to see how your cancer is responding. After your main treatment finishes, you will have follow-up visits and phone calls to monitor your health and cancer. The number of visits and checks will depend on your health and how long you received treatment.