Thymic Neuroendocrine Tumors

Abstract

Thymic neuroendocrine tumors are classified into four types; carcinoid, atypical carcinoid, large cell neuroendocrine carcinoma and small cell neuroendocrine carcinoma. According to classical commentary, these tumors are characterized by argyrophil and the presence of neurosecretory granules on electronmicroscopy. But now, the immunohistochemical methods demonstrate the neuroendocrine markers such as chromogranin A, synaptophysin, neuron-specific enolase and so on. Atypical carcinoids appear more common in the thymic tumors and show more aggressive biologic behavior than carcinoid tumors arising in other organs. Histogenetically, the famous hypothesis "APUDoma" proposed by Pears et al. is now considedered not acceptable recently. Thymic neuroendocrine tumors are not believed to be of neural crest origin. These tumors might have common origin with thymoma and thymic carcinoma and develop from epithelial stem-cell with the neuroendocrine differentiation.