Testing the Addition of an Anticancer Drug, Olaparib, to the Usual Chemotherapy (Temozolomide) for Advanced Neuroendocrine Cancer

This phase II trial studies how well the addition of olaparib to the usual treatment, temozolomide, works in treating patients with neuroendocrine cancer (pheochromocytoma or paraganglioma) that has spread from where it first started (primary site) to other places in the body (metastatic) or cannot be removed by surgery (unresectable). Poly (adenosine diphosphate \[ADP\]-ribose) polymerases (PARPs) are proteins that help repair deoxyribonucleic acid (DNA) mutations. PARP inhibitors, such as olaparib, can keep PARP from working, so tumor cells can\'t repair themselves, and they may stop growing. Chemotherapy drugs, such as 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 olaparib with temozolomide may shrink or stabilize the cancer in patients with pheochromocytoma or paraganglioma better than temozolomide alone.