CD99 positivity and EWS-FLI1 gene rearrangement identify a breast tumor in a 60-year-old patient with attributes of the Ewing family of neoplasms.

Rearrangements of the EWS gene with ETS transcription factor genes as a result of chromosomal translocation and high expression levels of CD99MIC2 characterize the Ewing family of tumors (EFT). This group of rather undifferentiated neoplasms affects bone and soft tissue in children and young adults mostly between 5 and 30 years of age (median, 15 years). This study reports a case of a CD99MIC2 positive small round cell tumor in the breast of a 60-year-old woman in whom a t(11;22)(q24;q12) chromosomal aberration was identified by cytogenetic analysis. Reverse transcriptase (RT)-polymerase chain reaction (PCR) followed by sequence analysis revealed expression of a chimera transcript in which EWS exon 10 was fused to FLI1 exon 6. Previously, this gene fusion has been reported to occur in approximately 3% of EFT. The specific gene rearrangement of EWS intron 10 was confirmed on Southern blot of genomic DNA. This study further contributes to the growing list of unusual neoplasms in adults that carry genotypic and phenotypic traits of the EFT.