What is a Neuroendocrine Tumor?

Pancreatic neuroendocrine tumors (PNET) are a rare subgroup of tumors found in the pancreas and can be either functional or non-functional.  Their appearance in histology sections has little to contribute to their malignant potential since this traditionally depends on the extent of their spread. However, recent WHO classification classifies PNET into well differentiated tumors, well differentiated carcinomas and poorly differentiated carcinomas in an attempt to predict natural history from the pathology report.

They are usually sporadic but they may also appear among other features of genetic syndromes like multiple endocrine neoplasia type I or von Hippel-Lindau disease.  Patients usually present with syndromes induced by hormones secreted from functional tumors, or with mass effects from nonfunctional tumors.  Functional PNET can secrete biologically active peptides like insulin, gastrin, glucagon, somatostatin, vasoactive intestinal polypeptide (VIP), whereas non-functional tumors also express and secrete peptides like neurotensin or chromogranin A, which are not active.

Most of the PNET are already metastatic by the time they are diagnosed and liver is the most common site of metastasis.  Regional lymph node spread is also common.  PNET are non-functional in their majority and the absence of a distinct functional syndrome as well as their indolent course and subsequent delay in diagnosis is mainly responsible for the advanced stage at the time of diagnosis.  PNET have a 5-year survival that can range from 97% in benign insulinomas to as low as 30% in non-functional metastatic PNET.  In addition, more recent data demonstrate that poorly differentiated PNET can have similar prognosis with adenocarcinomas of the gastrointestinal tract.

Surgery with curative intent is the mainstay of treatment for localized or loco-regional disease.

Surgery as well as other forms of local treatment like transarterial chemoembolization or radiofrequency ablation can also improve prognosis in patients with liver metastases [2, 4, 5].  For the inoperable cases, cytotoxic therapy with compounds like streptozotocin, 5-fluorouracil or doxorubicin can achieve modest outcome [6, 7, 8, 9].  Treatment with somatostatin analogues like octreotide has been proven to prolong progression-free survival in patients with metastatic neuroendocrine tumors of midgut origin.

This is a review of the recent advances in PNET as they were reported in four abstracts presented at the 2010 ASCO Gastrointestinal Cancers Symposium.