Carbonic anhydrase 9 expression in well-differentiated pancreatic neuroendocrine neoplasms might be associated with aggressive behavior and poor survival.

Well-differentiated pancreatic neuroendocrine neoplasms/tumors (PanNETs) are rare neoplasms with diverse clinical behavior. Biomarker discovery is important for predicting clinical course and prognosis of PanNET patients. Carbonic anhydrase 9 (CA9) and vimentin are hypoxia and epithelial-mesenchymal transition-related proteins of which expression in many carcinomas has been associated with poor prognosis, but their significance in PanNET has yet to be determined. We assessed CA9 and vimentin expression in 164 PanNETs and compared this with clinicopathologic characteristics. CA9 expression was observed in normal islets, while neuroendocrine microadenomas and small (< 1 cm) PanNETs showed loss of CA9 expression. CA9 and vimentin expression was observed in 38 (23%) and 36 (22%) of PanNETs, respectively. CA9 expression was associated with larger size (p = 0.001), higher grade (p < 0.001), higher pT category (p < 0.001), lymph node (p = 0.003) and distant (p = 0.047) metastases, higher AJCC stage (p < 0.001), and lymphovascular (p < 0.001) and perineural (p = 0.002) invasion. PanNET patients with CA9 expression had a shorter recurrence-free survival (5-year survival rate 47%) than those without CA9 expression (76%) by univariate (p = 0.001) but not multivariate analysis. Vimentin expression correlated with CA9 expression (p < 0.001) but not with other clinicopathologic factors. In conclusion, CA9 expression was observed in normal islets, while neuroendocrine microadenomas and small (< 1 cm) PanNETs showed CA9 expression loss. CA9 expression gradually reappeared in larger PanNETs, and this was associated with clinical progression and decreased patient survival by univariate but not multivariate analysis.