<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>A slow-growing type of tumor usually found in the gastrointestinal system (most often in the appendix), and sometimes in the lungs or other sites. Carcinoid tumors may spread to the liver or other sites in the body, and they may secrete substances such as serotonin or prostaglandins, causing carcinoid syndrome.</n0:def-definition><n0:def-source>NCI-GLOSS</n0:def-source></n0:ComplexDefinition><n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>A neuroendocrine neoplasm arising from enterochromaffin cells in the gastrointestinal tract and (less common) the bronchi with undetermined malignancy status.</n0:def-definition><n0:def-source>CDISC</n0:def-source></n0:ComplexDefinition>
<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>A slow growing neuroendocrine tumor, composed of uniform, round, or polygonal cells having monotonous, centrally located nuclei and small nucleoli, infrequent mitoses, and no necrosis. The tumor may show a variety of patterns, such as solid, trabecular, and acinar. Electron microscopy shows small secretory granules. Immunohistochemical studies reveal NSE, as well as chromogranin immunoreactivity. Malignant histology (cellular pleomorphism, hyperchromatic nuclei, prominent nucleoli, necrosis, and mitoses) can occasionally be seen. Such cases may have an aggressive clinical course. Gastrointestinal tract and lung are common sites of involvement.</n0:def-definition><n0:def-source>NCI</n0:def-source></n0:ComplexDefinition>