Novel Molecular Targets for the Treatment of Gastroenteropancreatic Endocrine Tumors: Answers and Unsolved Problems

As more knowledge on molecular alterations favoring carcinogenesis and spreading of gastroenteropancreatic endocrine tumors has become available, a number of targeted agents interfering with key growth and angiogenic pathways have been explored in preclinical and clinical studies. The mTOR inhibitor Everolimus, and the multi-target antiangiogenetic agent Sunitinib, have been shown to be effective and thus have been approved by the FDA for treatment of pancreatic endocrine tumors. However, there is little data on the primary resistance to targeted agents on these tumors. The goals of the present review are to elucidate the possible advantage of combined treatments in overcoming induced resistances, and to identify biomarkers able to predict clinical efficacy. Moreover, the role of interesting targets for which a strong biological rationale exists, and specific inhibitors are available, such as the Src Family Kinases and the Hedgehog Pathway, are discussed. There is now need for more preclinical studies on cell lines and animal models to provide a stronger preclinical background in this field, as well as clinical trials specifically comparing one targeted therapy with another or combining different targeted agents.