CD99, a traditional cell surface marker associated with Ewing sarcoma, was equally expressed in EWSR1-NFATc2 compared to EWSR1-ETS positive sarcomas, but lowly expressed in CIC-DUX4 positive sarcomas (mean ± SD: EWSR1-NFATc2 12.3 ± 0.6; CIC-DUX4 11.2 ± 1.0; EWSR1-ETS 12.3 ± 0.4; EWSR1-NFATc2 vs. EWSR1-ETSp = 0.81; EWSR1-NFATc2 vs. CIC-DUX4p = 0.02; CIC-DUX4 vs. EWSR1-ETSp < 0.0001; Supplementary Fig. 2B). Here, DUX4 is linked to Ewing sarcoma.