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Neuroendocrine carcinoma of the posterior mediastinum: a possible primary lesion.

A paravertebral mass was noted in the posterior mediastinum in a 47-year-old man. Microscopically, the tumor showed solid and trabecular patterns and consisted of poorly differentiated atypical cells that often formed Flexner-Wintersteiner rosettelike glands. Immunohistochemically, the tumor cells expressed both epithelial and neuroendocrine markers, including cytokeratin (AE1/3), carcinoembryonic antigen, epithelial membrane antigen, neuron-specific enolase, chromogranin A, and synaptophysin, but were negative for CD99 (MIC2). Ultrastructurally, numerous desmosomes and neurosecretory granules were identified in the tumor cells. The present lesion was a primary neuroendocrine carcinoma of the posterior mediastinum-an unusual site for such a lesion.