Specific expression of ZO-1 and N-cadherin in rosette structures of various tumors: possible recapitulation of neural tube formation in embryogenesis and utility as a potentially novel immunohistochemical marker of rosette formation in pulmonary neuroendocrine tumors.

Neuroendocrine tumors can develop in various organs. All of these tumors are designated on the basis of their morphologic characteristics evident by light microscopy, and by immunohistochemistry for antigens such as synaptophysin, chromogranin-A, and CD56/NCAM. In the present study, we attempted to demonstrate the localization of Zonula occludens-1 (ZO-1) and N-cadherin in rosette structures of neuroendocrine tumors using immunohistochemistry and to clarify their specific distribution in rosettes in human pulmonary neuroendocrine tumors in comparison with various types of adenocarcinoma. Among 40 neuroendocrine tumors of the lung examined, 18 cases (45%) and 22 cases (55%) were positive for ZO-1 and N-cadherin, respectively. In addition, we divided the cases into two types: 16 cases of Flexner-type tumor and 24 cases of Homer-Wright-type tumor. We then determined the Rosette Index (RoI; the percentage fraction of rosette structures positive for ZO-1 or N-cadherin among the total number of rosette structures). The Flexner-type neuroendocrine tumors showed significantly higher levels of RoI in ZO-1 than the Homer-Wright-type neuroendocrine tumors (median; 38.8% vs 0%, p < 0.001). On the other hand, N-cadherin and ZO-1 were hardly detected in tubular adenocarcinomas in various organs, and their immunoreactivities differed significantly between adenocarcinoma and pulmonary neuroendocrine tumor (ZO-1, mean 0.23% vs 18%, p < 0.0001; N-cadherin, mean 0% vs 33%, p < 0.0001). In conclusion, expression of ZO-1 and N-cadherin may reflect the mechanisms leading to rosette formation in neuroendocrine tumors, which possibly recapitulate neural tube formation in embryogenesis and could represent a specific immunohistochemical marker for neuroendocrine carcinoma of the lung.