Fig. 2

Histology of the nodule. The definitive histological examination of the nodular lesion, showed a tumor with an organoid pattern (a). At immunohistochemical staining, the cell population was positive for NSE, chromogranin, synaptophysin, natural killer cell-associated antigens CD56 and CD57, GFAP, and negative for CK, EMA, TTF-1 (b, c, d); the protein s100 has marked the base of the nests’ neoplastic cells (e). CK cytokeratin, EMA epithelial membrane antigen, GFAP glial fibrillary acid protein, NSE neuron-specific enolase, TTF-1 thyroid transcription factor-1