CD99 and neoplasm: Immunohistochemically, tumor cells demonstrated membranous positivity for CD99, positivity for Nkx2.2 (Fig. 4d and e), focal positivity for S100 and negativity for desmin, myogenin, MyoD1, cytokeratin (AE1/AE3), CD31, CD34, CD3, CD20, and CD1a.