This study is testing a new treatment called RYZ101 for a specific type of cancer called gastroenteropancreatic neuroendocrine tumors (GEP-NETs). These tumors have grown even after a previous treatment called 177Lu-SSA therapy. This study has two parts: the first part checks if RYZ101 is safe and how it moves through the body (pharmacokinetics, or PK). The second part compares RYZ101 to the standard treatment doctors usually use.

• The study is for people who can't have surgery and whose cancer has certain features in scans.
• You will need to have good kidney and blood function to join.
• The study excludes people with certain heart problems, uncontrolled high blood pressure, or diabetes.

Participation involves multiple visits to the study site for treatment and check-ups. It's important to know that certain health problems, like significant heart disease or not well-controlled diabetes, mean you can't join. This study helps researchers understand if RYZ101 can be a better or safer option than current treatments.