Neuroendocrine tumors (NETs) produce various hormones and bioactive substances and are known to express a large variety of peptide hormone receptors. While these hormones and receptors play a role in the pathophysiology of this heterogeneous group of tumors, they also form an important target for treatment and diagnosis. One of the most well-known target receptors in NETs are somatostatin receptors. On the basis of the expression of functional somatostatin receptors on the cell surface of NET cells, somatostatin analogs have already been used for decades to control symptoms related to hormonal overproduction in patients with NETs. Recent placebo-controlled studies have also demonstrated a significant antitumor activity, both in functioning and nonfunctioning NETs. Moreover, other peptide hormone receptors (e.g. receptors for GLP-1, CCK, GRP, secretin and dopamine) can be expressed at a high density in NETs. As such, these classes of receptors may also form potential targets for diagnosis and treatment. Finally, in recent years novel biotherapies targeting several growth factor systems have been introduced in the treatment of patients with NETs and are being explored for their efficacy in this setting, either as monotherapy or in combination treatment. This chapter aims to give an overview on the above topic.
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