A Study to Compare Zolbetuximab (IMAB362) and Chemotherapy With Placebo and Chemotherapy in Adults With Gastric Cancer.

This study is for adults over 18 who have advanced stomach cancer or cancer where the food pipe meets the stomach. This means your cancer has either spread to nearby tissues and can't be removed by surgery, or it has spread to other parts of your body. An important part is that a sample of your cancer must show a specific protein called Claudin 18.2.

You might be able to join if you haven't had chemotherapy for your cancer before, even if you've had other standard treatments. However, there are some reasons you wouldn't be able to take part. For example, if you need medicines to lower your immune system, if you have blockages or bleeding in your gut, certain uncontrolled cancers (like those affecting your nervous system that are causing symptoms), or if you have a specific heart condition or infections.

Also, if you are a woman who could become pregnant, you'll need to use birth control during and for a period after the study. The same applies to men who have female partners who could become pregnant. This is to ensure safety as the study medicines could affect a developing baby.

If you decide to take part, you will receive one of two study treatments by chance: either zolbetuximab with chemotherapy, or a dummy medicine (placebo) with chemotherapy. You, and your study doctor, won't know which one you are receiving – this is called 'double-blinded'. Both zolbetuximab and the placebo are given through a drip into a vein. This treatment happens in cycles.

Typically, each cycle lasts 6 weeks (42 days). You'll receive zolbetuximab or placebo twice per cycle, and chemotherapy (called modified FOLFOX6) three times per cycle. The first chemotherapy dose in each cycle is given on the same day as zolbetuximab or placebo. You could continue receiving zolbetuximab or placebo until your cancer gets worse, you can't tolerate the treatment, or you need different cancer treatment. The mFOLFOX6 chemotherapy will be given for up to 6 months. After 6 months, you might switch to another type of chemotherapy, which could continue for longer.

You'll have regular visits to the clinic for treatments, health checks, and to see if you have any side effects. You'll also have scans periodically to monitor your cancer. After you stop study treatment, you'll continue to have clinic visits, scans, and phone check-ups for a certain period to monitor your health and cancer over time.