Neuroendocrine malignancies such as pancreatic neuroendocrine tumors (PNETs) and gastrointestinal (GI) carcinoids, are generally rare but their incidences are increasing. In vitro and in vivo studies have shown that proteasome inhibitors have activity against a variety of tumor types. Carfilzomib (Kyprolis®) is an irreversible proteasome inhibitor with a favorable safety profile that has been studied in a variety of hematologic and solid tumors. Carfilzomib received accelerated approval from the U.S. FDA in 2012, based on a favorable response rate, for the treatment of patients with multiple myeloma who received at least two prior therapies, and demonstrated disease progression within 60 days of completing the last therapy. In this multi-center study, the investigators propose to evaluate carfilzomib for the treatment of patients with advanced neuroendocrine cancers.