mTOR Activation in Well Differentiated Pancreatic Neuroendocrine Tumors: A Retrospective Study on 34 Cases

Background/Aims: Pancreatic neuroendocrine tumors (PNET) are heterogeneous tumors with dramatically different prognosis. The survival is poor in patients with locally advanced or metastatic tumors. This study investigated expression and activation of mTOR in well differentiated PNET, and the relationship between mTOR activation and patients' clinicopathological characteristics. Methodology: Thirty-four samples were collected from patients who underwent surgery and had pathologically confirmed well differentiated PNET in Ruijin hospital from 2003 to 2009. All patients were classified based on 2010 WHO classification criteria and followed-up for survival. mTOR and phosphorylated-mTOR (p-mTOR) expressions were investigated by immunohistochemistry. Results: All 34 PNET patients received radical surgical resection, with 1 patient receiving adjuvant chemotherapy. Twenty-five patients were classified as NET G1, and 9 were NET G2. mTOR and p-mTOR expression rates were 70.6% and 61.8%, respectively. p-mTOR positive rate correlated with the WHO classification, the patients classified as NET G2 had higher p-mTOR positive rates (p=0.012). However, a significant correlation between p-mTOR positivity and selected clinicopathological characteristics, was not observed. Twenty-six patients were followed-up for a median time of 16.8 months, but a significant correlation between mTOR activation and patients' prognosis was also not observed. Conclusions: The expression of mTOR and p-mTOR is extensive in well differentiated PNET patients. Patients classified as NET G2 had a higher mTOR activation rate.