This study is testing a new medicine called TST001 for people with certain cancers that are hard to treat, like stomach, gastroesophageal, or pancreatic cancer. TST001 is a special kind of medicine called a monoclonal antibody, which is designed to target cancer cells. The study has two main parts:

• Part A: This part helps find the right dose of TST001. People will get the medicine every 2 or 3 weeks. Up to 36 people can join.
• Part B: This part divides people into three groups based on their cancer type and treatment history. They will receive TST001 with other cancer medicines. Each group can have up to 42 participants.

The study is for adults 18 years or older with advanced cancer. People cannot join if they have certain health problems, like specific heart diseases or untreated infections. The study will check how safe the medicine is and how well it works. Participants may need to visit the clinic regularly to receive the treatment and for check-ups.

• Participation includes regular visits for treatment and check-ups.
• Participants must be 18 or older with specific cancers.
• Certain health conditions may prevent participation.

Joining is a choice, and it's important to talk to a doctor about risks and benefits.