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

This is a Phase II study that will compare the effects, good and/or bad, of temozolomide versus temozolomide plus capecitabine on advanced pancreatic neuroendocrine tumors cancer to find out which is more effective. In this study, participants will get either temozolomide alone or temozolomide andcapecitabine. Temozolomide and capecitabine are chemotherapy drugs, which have benefited some patients with pancreatic neuroendocrine tumors yet they have never been compared; both arms are considered investigational. They are approved to treat several different types of cancer but have not been approved by the FDA to treat pancreatic neuroendocrine cancer. In addition to learning more about these chemotherapy drugs, this study will also evaluate certain molecular features of your pancreatic neuroendocrine cancer. Previously collected tumor tissue will be tested for certain changes to your tumor DNA. Investigators will specifically be looking for changes in a gene called MGMT to see if these changes predict for response to temozolomide. About 145 people will take part in this study.