Ewing sarcoma is the second most common malignant bone tumor in children and young adults. Cytogenetic analysis to identify a common t(
11;22)(
q23;q
12) or less frequently a t(2
1;22)(q22;q
12) or t(7;22)(p22;q
12) plays an important role in the confirmation of the clinical diagnosis. We report a case of a
10-year-old female who had extraskeletal Ewing sarcoma. Conventional cytogenetic analysis revealed that
11 out of 20 cells had a derivative chromosome 22, possibly due to an insertion of the long arm of the 2
1q2
1q22. This finding was confirmed by fluorescence in situ hybridization (FISH) utilizing whole chromosome paint probes specific for chromosomes 2
1 and 22. Hybridization utilizing LSI EWSR
1, dual-color break-apart rearrangement probe unexpectedly revealed that the 3′
EWSR1 gene was lost on the derivative chromosome 22. This finding suggests that the insertion of chromosome 2
1 is another mechanism that could lead to
EWS-ERG gene fusion. To our knowledge, this is the first case report of an insertion of a segment of 2
1q2
1q22 into the long arm of 2
1q
12 with a loss of a DNA segment around the breakpoint on the derivative chromosome 22 in Ewing sarcoma.