This study is for patients with advanced gastroenteropancreatic neuroendocrine tumors (GEP-NETs), which are rare types of cancer found in the stomach, intestines, or pancreas. The study compares two treatments: **[177Lu]Lu-DOTA-TATE** plus **octreotide LAR** versus octreotide LAR alone. **[177Lu]Lu-DOTA-TATE** is a type of targeted radiation therapy, and **octreotide LAR** is a long-acting medication that helps manage symptoms of neuroendocrine tumors by reducing hormone production. Patients joining the study must have a well-differentiated GEP-NET, which means the cancer cells look more like normal cells and usually grow and spread more slowly. Participants should be 12 years or older and have a high disease burden, meaning the cancer has spread significantly or causes severe symptoms. **Key Points:** - The study includes a screening phase, treatment phase, and follow-up phase. - Participants must not have had certain previous treatments or surgeries and should have adequate organ function. - Patients will need to visit the study site regularly for monitoring and treatment. This study aims to see if the combination treatment is more effective than octreotide LAR alone in managing advanced GEP-NETs.