Gastrointestinal neuroendocrine tumors.

Gastrointestinal neuroendocrine tumors (GI-NETs) are a genetically diverse group of malignancies that sometimes produce peptides causing characteristic hormonal syndromes. NETs can be clinically symptomatic (functioning) or silent (non-functioning); both types frequently synthesize more than one peptide, although often these are not associated with specific syndromes. Based on data from various sources the incidence and prevalence of GI-NETs is increasing. Surgery is the only possible curative approach and so represents the traditional first-line therapy. However, as most patients with NETs are diagnosed once metastases have occurred, curative surgery is generally not possible. Patients therefore require medical management with the aim of relieving symptoms and suppressing tumor growth and spread. Somatostatin analogues can improve the symptoms of carcinoid syndrome and stabilize tumor growth (PROMID study) in many patients. An antiproliferative effect can also be achieved with the m-TOR inhibitor everolimus, alone or in combination with octreotide LAR. The vascular endothelial growth factor inhibitor sunitinib has demonstrated antitumor effects in pancreatic NETs. Pasireotide, the multi-receptor targeted somatostatin analogue, has the potential to be an effective therapy for de novo or octreotide-refractory carcinoid syndrome. Peptide receptor radiotherapy with yttrium 90-DOTATOC or lutetium 177-DOTATE are also new interesting treatment options for NETs.