Maintenance Niraparib Plus Ipilimumab in Patients With Metastatic Pancreatic Adenocarcinoma Whose Disease Has Not Progressed on Platinum-Based Chemotherapy

The main goal of this study is to look at the effectiveness and anti-tumor activity (preventing growth of the tumor) of the drugs niraparib and ipilimumab, on the patients and their pancreatic cancer. This study will involve two different treatment arms. In Arm A, patients will receive niraparib plus ipilimumab. In Arm B, patients will receive standard chemotherapy. The main questions the study aims to answer are: * Does niraparib plus ipilimumab slow down tumor growth in patients with pancreatic cancer? * What medical problems do participants have when taking niraparib plus ipilimumab? Participants will: * Undergo screening procedures to evaluate their cancer, overall health, and suitability for the study * After passing screening, will be randomized to Arm A or B and be scheduled to receive niraparib plus ipilimumab (Arm A) or chemotherapy (Arm B) * Receive niraparib plus ipilimumab every 3 weeks (Arm A) * Receive chemotherapy every 2 weeks (Arm B) * Visit the clinic for regular checkups and tests