Translocation (11;22)(q24;q12) in a small cell tumor of the thigh in a 5-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 presen ted. Incisional biopsy was performed and subsequent histopathological exami nation revealed an infiltrative tumor composed of relatively large cells. T he tumor cells were immunoreactive for vimentin and keratin, but not for de smin 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 charac teristic 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 famil y of transcriptional regulators. Using reverse transcription polymerase cha in reaction (RT-PCR) a corresponding EWS-FLI-1 fusion product was detected. Additional immunohistological staining for p30/p32(MIC2), which is suggest ive, 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. N evertheless it was decided to treat the patient according to a Ewing's sarc oma protocol based on the genotype of the tumor. The findings were compared with other extraosseous pediatric small cell tumors showing the t(11;22)(q 24;q12) described in the literature. HUM PATHOL 30:352-355. Copyright (C) 1 999 by W.B. Saunders Company.