SYP and Ewing sarcoma: Histologic examination of Ewing's sarcoma typically reveals sheets of small, round, blue cells with a prominent nucleus and scant cytoplasm.5 Immunohistochemical findings, although not specific, include strong membrane expression of CD99 (also called MIC2), along with frequent expression of CD56 and synaptophysin; the absence of CD99 expression virtually rules out the diagnosis of Ewing's sarcoma.14’15