Silencing of UCHL1 by CpG Promoter Hyper-methylation is Associated with Metastatic Gastroenteropancreatic Well-Differentiated Neuroendocrine (Carcinoid) Tumors

Background. Well-differentiated gastroenteropancreatic neuroendocrine tumors (GEP-NETs) are rare tumors with varying metastatic potential. The underlying molecular basis for metastasis by GEP-NETs remains undefined. Methods. Quantitative PCR and immunohistochemistry (IHC) staining for ubiquitin carboxyl-terminal esterase L1 (UCHL1) gene and protein expression was performed on a group of localized and metastatic well-differentiated GEP-NET samples acquired from a prospectively maintained tissue bank. The ability of extent of UCHL1 IHC staining to differentiate localized and metastatic tumors was compared with Ki-67 index. Results. Among 46 total samples, UCHL1 expression at both the gene and protein level was significantly greater among localized GEP-NETs compared with metastatic tumors and metastases (p<0.001). Hypermethylation of the UCHL1 promoter was commonly observed among metastatic primary tumors and metastases (those with the lowest UCHL1 expression) but not among localized tumors (p<0.001). Poor staining (<50 %) for UCHL1 was observed in 27 % of localized tumors compared with 87 % of metastatic tumors (p = 0.001). The presence of <50 % staining for UCHL1 was 88 % sensitive and 73 % specific for identifying metastatic disease. In contrast, there was no association between Ki-67 index and metastatic disease. In multivariable analysis, only UCHL1 staining <50 % [odds ratio (OR) 24.5, p = 0.035] and vascular invasion (OR 38.4, p = 0.03) were independent risk factors for metastatic disease at the time of initial surgery. Conclusions. Loss of UCHL1 expression by CpG promoter hypermethylation is associated with metastatic GEPNETs. Extent of UCHL1 staining should be explored as a potentially clinically useful adjunct to Ki-67 index in evaluating GEP-NETs for aggressive features.