Fig. 4

Biopsy of tumor tissue. Microscopically, the Hematoxylin-Eoson (HE) staining showed sheets of “blue” tumor cells with prominent “pink” necrotic areas (a). The cells were relatively uniform and round with a high nucleocytoplasmic ratio and scanty clear cytoplasm (b). Immunostaining was diffusely positive for CD99 (c) and cytokeratin CAM5.2, focally positive for S-100 protein, and negative for cytokeratin AE1/AE3, CD3, CD20, CD56, synaptophysin, desmin and myoglobin. In light of the results of chromosomal analysis, additional staining for NUT protein was performed, and showed nuclear positivity (d)

A: HE staining × 20, B: HE staining × 200, C: CD99 × 100, D: NUT protein × 200