Translocation (11;22)(q24;q12) in a small cell tumor of the thigh in a 2-year-old boy: Immunohistology, cytogenetics, molecular genetics, and review of the literature

A case of a 2-year-old boy with a palpable mass in the left thigh is presented. Incisional biopsy was performed and subsequent histopathological examination revealed an infiltrative tumor composed of relatively large cells. The tumor cells were immunoreactive for vimentin and keratin, but not for desmin or smooth muscle actin. Cytogenetic analysis showed a 46,XY,t(11;22)(q24;q12) karyotype. The translocation (11;22)(q24;q12) is said to be characteristic for the family of Ewing's sarcoma and related tumors. As a result of the t(11;22)(q24;q12) the EWS gene on chromosome 22q12 joins the 3' part of FLI-1 gene on chromosome 11q24, which encodes a member of the ets family of transcriptional regulators. Using reverse transcription polymerase chain reaction (RT-PCR) a corresponding EWS-FLI-1 fusion product was detected. Additional immunohistological staining for p30/p32MIC2, which is suggestive, but not specific for Ewing's sarcoma, appeared to be weakly positive. In the current case a diagnosis of Ewing's sarcoma was considered unlikely, because of the location of the tumor and the immunohistological profile. Nevertheless it was decided to treat the patient according to a Ewing's sarcoma protocol based on the genotype of the tumor. The findings were compared with other extraosseous pediatric small cell tumors showing the t(11;22)(q24;q12) described in the literature