In nine cases of CIC-associated sarcoma, CD56 was expressed in five, alpha-smooth muscle actin in one, ERG in three, and CD99, WT1 and TLE1 each in eight cases.
NKX2-2 was positive in 37/40 (93%) Ewing sarcomas, including all atypical Ewing sarcomas and cases with known EWSR1-FLI1 or EWSR1-ERG fusion; 85% of Ewing sarcomas showed diffuse (>50%) staining.
All 3 CIC-rearranged AS cases lacked vasoformation and had a solid growth of round, epithelioid to rhabdoid cells, showing immunoreactivity for CD31 and Ets-related gene and sharing a transcriptional signature with other round cell sarcomas, including CIC-rearranged tumors.
ERG (Ets related gene) overexpression or increased activity has been found in various human cancers, including sarcomas, acute myeloid leukemia and prostate cancer, where the ERG gene is rearranged due to chromosomal translocations.
The EWS-ERG fusion protein is found in human sarcomas with the chromosomal translocation t(21;22)(q22;q12), where the translocation is considered to be an initiating event in sarcoma formation within uncommitted mesenchymal cells, probably long-lived progenitors capable of self renewal.