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Introduction: Neuroendocrine cells are widely distributed throughout the body, and neoplasms from these dispersed cells can arise at many sites. They are distinguished into two broad categories: 1) Tumors identified as small cell lung carcinomas with biology and natural history of a high-grade malignancy and characteristics of small cell undifferentiated or anaplastic appearance by light microscopy. The WHO categorizes these tumors as poorly-differentiated neuroendocrine carcinomas; 2) Well-defined neuroendocrine tumors (NETs) with variable, but most lyindolent biologic behavior and characteristic well-differentiated histologic features. The majority arise in the gastrointestinal tract and collectively they are referred as gastroenteropancreatic neuroendocrine tumors (GEP/NETs). They include carcinoid tumors, pancreatic islet cell tumors (gastrinoma, insulinoma, glucagonoma, VIPoma, somatostatinoma), paragangliomas, pheochromocytomas, and medullary thyroid carcinomas. The WHO classifies the GEP/NETs as well-differentiated NETs (carcinoid tumors) if they are noninvasive and have benign behavior or uncertain malignant potential. In contrast, GEP/NETs with characteristics of low-grade malignancy with invasion of the muscularis propria or beyond, or metastases, are characterized as well-differentiated neuroendocrine carcinomas (malignant carcinoids). Pancreatic islet cell tumors, whether functioning or not, are classified as well-differentiated NETs or well-differentiated neuroendocrine carcinomas, due to the (depending on) histologic characteristics. The WHO classification for gastroenteropancreatic NETs based on stage (ie size and presence of metastases) and grade (mitotic rate, perineural and lymphovascular invasion, Ki-67 proliferative index) categorizes them as well-differentiated NETs, e.g., carcinoid tumors, or as well-differentiated neuroendocrine carcinomas.
Conference: 7th Annual ENETS Conference (2010)
Presenting Author: Dr Michael M. Vaslamatzis