Abstract
Several important landmark trials have reshaped the landscape of non-surgical management of small bowel neuroendocrine tumors over the last few years, with the confirmation of the antitumor effect of somatostatin analogue therapy in PROMID and CLARINET trials as well as the advent of therapies with significant potential such as mammalian target of rapamycin inhibitor (mTor) everolimus (RADIANT trials) and peptide receptor radionuclide therapy (PRRT) with 177-Lutetium (NETTER-1 trial). This narrative summarizes the recommended management strategies of small bowel neuroendocrine tumors. We review the main evidence behind each recommendation as well as compare and contrast four major guidelines, namely the 2016 Canadian Consensus guidelines, the 2017 North American Neuroendocrine Tumor Society guidelines, the 2018 National Comprehensive Cancer Network guidelines, and the 2016 European Neuroendocrine Tumor Society guidelines. Different clinical situations will be addressed, from loco-regional therapy to metastatic unresectable disease. Carcinoid syndrome, which is mostly managed by somatostatin analogue therapy and the serotonin antagonist telotristat etiprate for refractory diarrhea, as well as neuroendocrine carcinoma will be reviewed. However, several questions remain unanswered, such as the optimal management of neuroendocrine carcinomas or the effect of combining and sequencing of the aforementioned modalities where more randomized controlled trials are needed.
Highlights
Neuroendocrine tumors (NETs) are a heterogeneous group of neoplasms arising from various anatomic sites, the majority originating from the small bowel or pancreas
Most small bowel neuroendocrine tumors are enterochromaffin cell tumors that make serotonin; because of the vascular drainage, the serotonin is inactivated in the liver, these tumors tend to be hormonally inactive until they develop extensive liver metastases, when the excess serotonin gives rise to carcinoid syndrome, a constellation of symptoms including flushing, diarrhea and right-sided heart failure
This differs from the clinical presentation of their pancreatic counterpart, where symptoms related to hormone over-secretion by the tumor can occur with even small localized tumors
Summary
Neuroendocrine tumors (NETs) are a heterogeneous group of neoplasms arising from various anatomic sites, the majority originating from the small bowel or pancreas. Most small bowel neuroendocrine tumors are enterochromaffin cell tumors that make serotonin; because of the vascular drainage, the serotonin is inactivated in the liver, these tumors tend to be hormonally inactive until they develop extensive liver metastases, when the excess serotonin gives rise to carcinoid syndrome, a constellation of symptoms including flushing, diarrhea and right-sided heart failure. This differs from the clinical presentation of their pancreatic counterpart (pancreatic neuroendocrine tumors, pNET), where symptoms related to hormone over-secretion by the tumor can occur with even small localized tumors. Consensus guidelines [12], the 2017 North American Neuroendocrine Tumor Society guidelines (NANETS) [13,14], the 2018 National Comprehensive Cancer Network guidelines (NCCN) [15] and the 2016 European Neuroendocrine Tumor Society guidelines (ENETS) [16,17]
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