Testing the Addition of An Anti-cancer Drug, M3814 (Peposertib), to the Usual Radiation-Based Treatment (Lutetium Lu 177 Dotatate) for Pancreatic Neuroendocrine Tumors

This phase Ib trial is to find out the best dose, possible benefits and/or side effects of peposertib when given together with lutetium Lu 177 dotatate in treating patients with neuroendocrine tumors. Peposertib may stop the growth of tumor cells by blocking some of the enzymes needed for cell formation, so as to help block the formation of growths that may become cancer. Radioactive drugs, such as lutetium Lu 177 dotatate, may deliver radiation directly to tumor cells and not harm normal cells. Adding peposertib to lutetium Lu 177 dotatate may kill more tumor cells.