Molecular pathology of pancreatic neuroendocrine tumors

Pancreatic endocrine tumors (PETs) are rare neoplasms which account for 1% to 2% of all pancreatic malignancies. The diagnostic, grading and prognostic criteria for PETs have been controversial in surgical pathology and clinical medicine. The newly updated 2010 WHO classification introduced in clinical practice will give more insight into genetic and molecular changes related to PET subtypes. These neoplasms can be graded into 1 of 3 tiers, based on histologic characteristics in likeness to epithelial neuroendocrine tumors in other anatomic sites. Most PETs are sporadic, however, some of them, may occur as part of familial tumors (inherited syndromes) such as multiple endocrine neoplasia type 1 (MEN1 syndrome), von Hippel-Lindau disease (VHL), neurofibromatosis type 1 (NF-1), and tuberous sclerosis (TSC). In sporadic endocrine pancreatic tumors, losses of chromosome 1 and 11q as well as gain on 9q appear to be early events in the development of pancreatic tumors. Multiple genetic defects may accumulate with time and result in pancreatic neuroendocrine tumor progression and malignancy. Although PETs may be similar or identical in histologic appearance to neuroendocrine tumors of the gastrointestinal tract, differences in their underlying biology and likely differences in response to therapeutic agents suggest that they should be treated and investigated as a distinct entity. The correlation of PI3K/Akt/mTOR pathway in the pathogenesis of PETs has been reported, and clinical trials data of mTOR inhibitors is promising.