Novel anticancer agents in clinical trials for well-differentiated neuroendocrine tumors

Neuroendocrine tumors (NETs) are rare malignancies that arise from endocrine cells located in various anatomic locations, with a dramatic increase in incidence during the last 30 years. Limited therapeutic options are currently available for patients with advanced well-differentiated NETs, including carcinoids and pancreatic NETs. Streptozotocin-based chemotherapy and somatostatin analogues are drugs that are currently used for the treatment of progressive metastatic NETs. Recently, sunitinib demonstrating efficacy in pancreatic islet cell carcinomas has opened a new avenue for the treatment of NETs, and further trials shall be considered in NET types such as carcinoids, poorly differentiated neuroendocrine carcinomas, and several other endocrine tumors that depend on vascular endothelial growth factor (VEGF)/VEGF receptor for angiogenesis. In addition, drugs with distinct mechanisms of action, such as mammalian target of rapamycin inhibitors, currently investigated in phase 3 trials, may also supply novel options to control tumor growth and metastasis. Although acknowledged as rare tumors, recent data demonstrated the feasibility of large randomized trials in this disease. Furthermore, data from large trials also showed the importance of selecting an appropriate patient population when designing randomized studies. This review focuses on novel therapeutic approaches in the treatment of well-differentiated NETs. Based on recent data, novel strategies may now be designed using those anticancer agents to optimize the current treatment of patients with NETs.