RecruitingDrug trialLu-177-DOTATATE (Lutathera) in Combination With Olaparib in Inoperable Gastroenteropancreatico Neuroendocrine Tumors (GEP-NET)Background: A neuroendocrine tumor is a rare type of tumor. It comes from body cells called neuroendocrine cells. Sometimes, these tumors develop in the gastrointestinal tract and pancreas. Researchers want to find out if a combination of drugs can shrink these tumors. Objective: To learn if people with certain neuroendocrine tumors can take a combination of 2 drugs, Lutathera and Olaparib, without having severe side effects, and if this treatment makes the tumors shrink. Eligibility: Adults 18 and older who have a neuroendocrine tumor in the pancreas or intestine that cannot be cured by surgery and has somatostatin receptors on the cells. Design: Eligible participants will get Lutathera through an intravenous (IV) infusion every 8 weeks for 4 cycles. One cycle is 8 weeks. Each cycle includes a follow-up visit at week 4. For the IV, a small plastic tube is put into an arm vein. Participants will also take Olaparib by mouth twice a day for 4 weeks of each cycle. They will use a medicine diary to track the doses. During the study, participants will have physical exams. They will have blood and urine tests. They will fill out questionnaires about their general well-being and function. Their heart function will be tested. They will have scans of their chest, abdomen, and pelvis. One type of scan will use an IV infusion of a radioactive tracer. Participants will have a follow-up visit about 4 weeks after treatment ends. Then they will have follow-up visits every 12 weeks for 3 years. Then they will have yearly phone calls.