Abstract 4087: Epithelial to mesenchymal transition in the metastatic progression of gastroenteropancreatic neuroendocrine tumors
Authors: Mok Stephanie , Khan Zia A. , Quan Douglas , Howlett Christopher J. 
Published: August 2015

Abstract
Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) are malignant epithelial cancer arising from the diffuse neuroendocrine system. Diagnosis is usually made late in the disease course, with 60-80% of diagnosed cases presenting with, or developing metastatic disease. The lack of biomarkers indicative of aggressive behavior, in particular metastasis, hinders prognosis and proper treatment of GEP-NETs. A cellular process underlying the aggressive behavior of cancer is epithelial to mesenchymal transition (EMT). In this study, we aimed to determine whether EMT is involved in the pathogenesis of NETs. Using tissue samples from NETs arising from small intestine (SI-NET), pancreas (P-NETs), and colorectum (C-NETs), we have examined EMT and profiled the signaling mechanisms involved.
Initial studies utilizing targeted real-time PCR-based gene profiling comparing primary (n = 9) and metastatic (n = 4) SI-NETs relative to control (normal small bowel epithelium, n = 3) revealed gene expression profiles suggestive of EMT and cell guidance in both primary and metastatic tumors, including elevation of vascular endothelial growth factor signaling, changes in matrix remodeling genes, and abundant transforming growth factor-β (TGF-β) receptor 1. A more comprehensive examination of the EMT phenotype was then undertaken based on primary site of origin. RNA samples from P-NETs (n = 9), SI-NETs (n = 8), and C-NETs (n = 8) were used for gene expression studies utilizing an EMT-focused PCR array. Changes in gene expression profiles consistent with an EMT phenotype were seen across all primary sites, including elevated expression of transcription factors SMAD2, ZEB1/2, HIF-1α. Differential expression of TGF-β family receptor ligands, including TGF-β1 and BMP2, was observed when comparing results from NETs of different primary sites, suggesting alternate signaling pathways leading to EMT. Confirmatory immunohistochemistry studies were then carried out, demonstrating an EMT phenotype as evidenced by loss of E-cadherin/β-catenin expression and/or vimentin induction in 42% of cases (n = 52).
Well-differentiated GEP-NETs, while morphologically similar, are extremely heterogeneous in both clinical presentation and outcome. We have examined a series of 52 GEP-NETs, of which 77% either presented with, or eventually developed metastatic disease. EMT is likely a key process by which this occurs, as we observe expression changes in EMT-associated genes across all subtypes of GEP-NETs, and an EMT phenotype by immunohistochemistry in 42% of the tumors. Our gene expression studies suggest that differential TGF-β family signaling is a key mediator in driving EMT, however, the specific pathway may involve different factors depending on the site of NET origin. Future studies are needed to elucidate the exact pathways involved in this process.
Citation Format: Stephanie Mok, Zia A. Khan, Douglas Quan, Christopher J. Howlett. Epithelial to mesenchymal transition in the metastatic progression of gastroenteropancreatic neuroendocrine tumors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4087. doi:10.1158/1538-7445.AM2015-4087