This phase III trial compares perioperative chemotherapy (given before and after surgery) versus adjuvant chemotherapy (given after surgery) for the treatment of pancreatic cancer that can be removed by surgery (removable/resectable). Chemotherapy drugs, such as fluorouracil, irinotecan, leucovorin, and oxaliplatin, work in different ways to stop the growth of tumor cells, either by killing the cells, by stopping them from dividing, or by stopping them from spreading. Giving chemotherapy before and after surgery (perioperatively) may work better in treating patients with pancreatic cancer compared to giving chemotherapy after surgery (adjuvantly).

This phase II trial investigates how well the addition of olaparib following completion of surgery and chemotherapy works in treating patients with pancreatic cancer that has been surgically removed (resected) and has a pathogenic mutation in BRCA1, BRCA2, or PALB2. Olaparib is an inhibitor of PARP, an enzyme that helps repair deoxyribonucleic acid (DNA) when it becomes damaged. Blocking PARP may help keep tumor cells from repairing their damaged DNA, causing them to die. PARP inhibitors are a type of targeted therapy.

This phase II trial studies whether adding pembrolizumab to olaparib (standard of care) works better than olaparib alone in treating patients with pancreatic cancer with germline BRCA1 or BRCA2 mutations that has spread to other places in the body (metastatic). BRCA1 and BRCA2 are human genes that produce tumor suppressor proteins. These proteins help repair damaged deoxyribonucleic acid (DNA) and, therefore, play a role in ensuring the stability of each cell's genetic material. When either of these genes is mutated, or altered, such that its protein product is not made or does not function correctly, DNA damage may not be repaired properly. As a result, cells are more likely to develop additional genetic alterations that can lead to some types of cancer, including pancreatic cancer. Immunotherapy with monoclonal antibodies, such as pembrolizumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread. Olaparib is an inhibitor of PARP, a protein that helps repair damaged DNA. Blocking PARP may help keep tumor cells from repairing their damaged DNA, causing them to die. PARP inhibitors are a type of targeted therapy. The addition of pembrolizumab to the usual treatment of olaparib may help to shrink tumors in patients with metastatic pancreatic cancer with BRCA1 or BRCA2 mutations.

This phase II trial studies the effect of capecitabine and temozolomide after surgery in treating patients with high-risk well-differentiated pancreatic neuroendocrine tumors. Chemotherapy drugs, such as capecitabine and temozolomide, work in different ways to stop the growth of tumor cells, either by killing the cells, by stopping them from dividing, or by stopping them from spreading. Giving capecitabine and temozolomide after surgery could prevent or delay the return of cancer in patients with high-risk well-differentiated pancreatic neuroendocrine tumors.