Pancreatic neuroendocrine tumors: Signal pathways and targeted therapies

Pancreatic neuroendocrine tumors (PNETs) are rare but are well understood to cover a broad spectrum of clinical presentation, tumor biology and prognosis. More than 60% of PNETs are diagnosed at advanced disease stage and are ineligible for surgical resection. Prior to 2011, streptozocin was the only approved agent for unresectable advanced PNETs. In recent years, breakthroughs in signal pathway research have led to the identification of new therapeutic targets and agents directed at the molecular level. In 2011, two new targeted therapeutic agents, sunitinib and everolimus, were approved by the Food and Drug Administration (FDA). Sunitinib is an inhibitor of multiple tyrosine kinases, and everolimus is an inhibitor of the mammalian target of rapamycin (mTOR) pathway. This review discusses the major signaling pathways that are frequently mutated or deregulated in PNETs, and the implications of molecular alterations for PNET therapy. Biologic therapy through targeting relevant pathways represents a promising approach in the therapy of advanced and unresectable PNETs.