CD99 and neoplasm: In contrast to EES, tumor cells from 13/13 RMS cases were positive for nuMyoD1 and/or numyogenin, in the absence of CD10, CD105, and CD58 expression, showed variable percentages of CD90+ (5/13, 39%) and CD9+ (5/13, 39%) and heterogeneous levels of expression of GD2, CD57, and CD99 in 1/13 (7%) RMS case (Figure 3 and Table S2).