Neuroendocrine tumors of the diffuse neuroendocrine system

Neuroendocrine tumors (previously referred to as carcinoids) are ill-understood, enigmatic malignancies that, although slow-growing compared with adenocarcinomas, can behave aggressively. In 2004, they comprised 1.25% of all malignancies; their incidence is increasing by approximately 6% per year. The present review provides an overview on neuroendocrine tumors and focuses on general features and current diagnostic and therapeutic options.

Neuroendocrine tumors may present a considerable diagnostic and therapeutic challenge as their clinical presentation is nonspecific and usually late, when metastases are already evident. Topographic localization is by computed tomography, magnetic resonance imaging, somatostatin receptor scintigraphy, whole-body positron emission tomography or endoscopy/ultrasound. Bronchoscopy is useful to verify the diagnosis when lesions are located centrally in the bronchi. No curative treatment except for radical surgery (almost never feasible) exists. Palliative and symptomatic treatment is based on surgical debulking, tumor embolization, and biotherapy with somatostatin analogues. Chemotherapy and radiotherapy are usually ineffective, but novel drugs such as tyrosine kinase receptor inhibitors show promising results in phase II clinical studies.

Tumors of the diffuse neuroendocrine system represent a significant and increasing clinical problem, and there is a need to develop both early diagnostic tests as well as to establish targeted therapeutic strategies.