CD99 and neoplasm: By immunohistochemistry, the tumor cells expressed synaptophysin, chromogranin, NKX2.2 (diffuse, nuclear) (Fig. 2A), GFAP (patchy), SMI31 (neurofilament) (focal, cytoplasmic), and TdT (Fig. 2B) (diffuse, nuclear), while lacking expression of CD99, TTF-1, CK20, MCPyV, PHOX2B (Fig. 2C), Olig2, OCT3/4, CD45, CD3 and PAX5.