Pancreatic neuroendocrine tumor

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Pancreatic neuroendocrine tumors (PanNETs, PETs, or PNETs), often referred to as “islet cell tumors”, or “pancreatic endocrine tumors” are neuroendocrine neoplasms that arise from cells of the endocrine (hormonal) and nervous system within the pancreas.

PanNETs are a type of neuroendocrine tumor, representing about one third of gastroenteropancreatic neuroendocrine tumors (GEP-NETs). Many PanNETs are benign, while some are malignant. Aggressive PanNET tumors have traditionally been termed “islet cell carcinoma”.

PanNETs are quite distinct from the usual form of pancreatic cancer, the majority of which are adenocarcinomas, which arises in the exocrine pancreas. Only 1 or 2% of clinically significant pancreas neoplasms are PanNETs.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

PanNETs are sometimes abbreviated as PETs or PNETs: such use should not to be confused with the primitive neuroectodermal tumor (PNET).

The majority of PanNETs are benign, while some are malignant. The World Health Organization (WHO) classification scheme places neuroendocrine tumors into three main categories, which emphasize the tumor grade rather than the anatomical origin. In practice, those tumors termed well or intermediately differentiated PanNETs in the WHO scheme are sometimes called “islet cell tumors.” The high grade subtype, termed neuroendocrine cancer (NEC) in the WHO scheme, is synonymous with “islet cell carcinoma”.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

DNA mutation analysis in well-differentiated pancreatic neuroendocrine tumors identified four important findings:^[1][2]

• as expected, the genes mutated in NETs, MEN1, ATRX, DAXX, TSC2, PTEN and PIK3CA,^[1] are different from the mutated genes previously found in pancreatic adenocarcinoma.^[3][4]

• one in six well-differentiated pancreatic NETs have mutations in mTOR pathway genes, such as TSC2, PTEN and PIK3CA.^[1] The sequencing discovery might allow selection of which NETs would benefit from mTOR inhibition such as with everolimus, but this awaits validation in a clinical trial.

• mutations affecting a new cancer pathway involving ATRX and DAXX genes were found in about 40% of pancreatic NETs.^[1] The proteins encoded by ATRX and DAXX participate in chromatin remodeling of telomeres; these mutations are associated with a telomerase-independent maintenance mechanism termed ALT (alternative lengthening of telomeres) that results in abnormally long telomeric ends of chromosomes.

• ATRX/DAXX and MEN1 mutations were associated with a better prognosis.^[1]

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