The carcinoid syndrome: neuroendocrine and chemical considerations.

The carcinoid syndrome is characterized by a complex of neuroendocrine and chemical abnormalities whose cause is not known. Carcinoids vary in their tendency to produce the carcinoid syndrome, although ileal tumors and those that have metastasized are more frequently associated with manifestations of the syndrome. The unifying concept of a neural crest origin for these and related neoplasms provides a basis for understanding the hormonal and chemical features of this disease. The extent of the various hormonal changes is only now becoming apparent and will undoubtedly expand as investigation continues in this area.