Temozolomide With or Without Capecitabine in Treating Patients With Advanced Pancreatic Neuroendocrine Tumors

Inclusion Criteria: * Patient must have histologically or pathologically confirmed locally unresectable or metastatic low or intermediate grade pancreatic neuroendocrine tumor * Patient must have measurable disease by Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 criteria; baseline measurements and evaluations of all sites of disease must be obtained \<= 4 weeks prior to randomization and must be acquired by multiphasic CT or contrast magnetic resonance imaging (MRI) * Date of last documented disease progression must be within 12 months from date of randomization * Prior everolimus and/or sunitinib therapy is allowed, so long as it was discontinued \>= 4 weeks prior to randomization * Concurrent somatostatin analogues are allowed provided that patients * Have been on a stable dose for 8 weeks and * Have documented disease progression on that dose * Chemoembolization is allowed if ≥ 4 weeks from study entry. There are 2 possible scenarios: * If patient has hepatic disease only: they need to have progressed in the liver since chemoembolization and have measurable disease by RECIST 1.1 in order to be eligible. * If patient has hepatic and extrahepatic disease: they will need to have progressed inside OR outside the liver and have measureable disease by RECIST 1.1 in order to be eligible. * Leukocytes \>= 3,000/mm\^3 * Absolute neutrophil count \>= 1,500/mm\^3 * Hemoglobin \>= 9 g/dL * Platelets \>= 100,000/mm\^3 * Total bilirubin \<= institutional upper li…