Analysis of molecular pathways in sporadic neuroendocrine tumors of the gastro-entero-pancreatic system.
ABSTRACT Little is known about the molecular pathogenesis of neuroendocrine tumors (NET) of the gastro-entero-pancreatic (GEP) system. We analyzed genetic and epigenetic alterations as well as the CpG island methylator phenotype (CIMP). The study comprised 118 well-differentiated fore- and mid-gut GEP-NET from 71 patients. In addition to loss of heterozygosity (LOH), microsatellite instability (MSI) and the methylation status of various tumor associated genes were examined. The expression profile of p16, APC and MENIN was investigated by immunohistochemistry. None of the tumors was highly microsatellite unstable, LOH was found in 22.2%. Significant differences in promoter hypermethylation were identified in the RUNX3 and the O(6)-MGMT genes. We found a significant loss of p16 expression in insulinomas (p = 0.05) and functional NET (p = 0.01), respectively. APC was expressed less in gastrinomas (p = 0.01) and functional GEP-NET (p = 0.05) vs. nonfunctional tumors. MENIN expression was reduced in pancreatic vs. extrapancreatic NET (p = 0.008) and in insulinomas vs. nonfunctional GEP-NET (p = 0.019) and NET associated with the carcinoid syndrome (p = 0.029). Further CIMP and a Ki-67 index >10% showed a close correlation. Outcome analysis of 19 patients showed a better survival for CIMP-negative patients. The analyses identified significant genetic and epigenetic alterations in well-differentiated fore- and mid-gut NET. CIMP, similar to Ki-67, might turn out to be of prognostic relevance.
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Article: Hereditary colorectal cancer.New England Journal of Medicine 04/2003; 348(10):919-32. · 51.66 Impact Factor
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ABSTRACT: About 15% of all colorectal cancers (CRCs) demonstrate high levels of microsatellite instability (MSI-H) and are currently best identified by molecular analysis of microsatellite markers. Most sporadic CRCs with MSI-H are known to be associated with the methylation of the hMLH1 promoter. Promoter methylation coincided with lack of hMLH1 expression. We aimed to investigate the association between MSI status, hMLH1 protein expression and methylation status of the hMLH1 promoter, and to determine the usefulness of each method in defining the MSI phenotype in sporadic CRCs. CRCs from 173 patients from the Cancer and Leukemia Group B (CALGB) were assessed for their MSI status. An additional cohort of 18 MSI-H tumors from the University of California San Diego (UCSD) was included in the analysis of the MSI-H subgroup. MSI testing was performed by PCR using five standard MSI markers. hMLH1 promoter analysis was investigated by methylation specific PCR (MSP), and expression of the MMR genes hMLH1 and hMSH2 was examined by immunohistochemistry (IHC). Of the 173 CALGB tumors, 111 (64%) were MSS, 35 (20%) were MSI-L and 27 (16%) MSI-H, respectively. Data on hMLH1 protein expression, hMSH2 protein expression and hMLH1 methylation are available on 128, 173 and 81 of these tumors, respectively. Presence of hMLH1 and hMSH2 protein expression was significantly associated with MSI status. Four of 45 (8.9%) MSI-H tumors and 0 of 146 (0%) MSS/MSI-L tumors did not express hMSH2 (p = 0.0028). hMLH1 protein expression was present in 107 of 108 (99%) MSS and MSI-L tumors versus 11 of 20 (55%) MSI-H tumors (p < 0.0001). Of 61 MSS and MSI-L cancers studied for methylation, 11 (18%) were methylated at the hMLH1 promoter whereas 14 of 20 (70%) MSI-H cancers were methylated (p = 0.0001). In 27 MSI-H tumors studied for hMLH1 protein expression and methylation, 93% of tumors with loss of expression (93%) were also methylated while 42% (5/12) with positive immunostaining for hMLH1 were methylated at the hMLH1 promoter (p = 0.009). Promoter methylation and hMLH1 expression are significantly associated with the MSI-H phenotype in CRC. Promoter methylation analysis provides a useful means to screen for MSI-H tumors. Our data further suggests that hMLH1 promoter methylation analysis alone cannot replace MSI testing, as a significant number of MSI-H tumors could be potentially overseen by such an approach. We suggest that phenotypic evaluation of CRC is performed most reliably with MSI testing, although expression analysis and investigation of the promoter methylation status may complement the screening process.Cancer biology & therapy 01/2004; 3(1):73-8. · 3.29 Impact Factor
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ABSTRACT: E-cadherin, a M(r) 120,000 transmembrane glycoprotein, mediates calcium-dependent intercellular adhesion that is essential for normal tissue homeostasis. Loss of E-cadherin occurs in a variety of epithelial tumors and is correlated with invasion and metastasis. In esophageal adenocarcinoma, reduction of E-cadherin expression has been demonstrated previously, but mutations of the gene (CDH1) are rare. In this study, we used a nested PCR approach to examine the methylation status of the 5' CpG island of E-cadherin in esophageal specimens obtained from individuals with and without a history of esophageal cancer. In four individuals without esophageal cancer, E-cadherin was completely unmethylated in normal squamous cell-lined esophageal mucosa. In contrast, in patients with esophageal adenocarcinoma, E-cadherin was methylated in 26 of 31 (84%) tumor specimens. In the majority of cases, matched normal tissue (esophagus or stomach) from each patient was completely unmethylated. By immunostaining, methylated tumor samples demonstrated heterogeneously decreased membranous E-cadherin staining. These data suggest that epigenetic silencing via aberrant methylation of the E-cadherin promoter is a common cause of inactivation of this gene in esophageal adenocarcinoma.Clinical Cancer Research 10/2001; 7(9):2765-9. · 7.84 Impact Factor