Ewing sarcoma of the small bowel : a study of seven cases, including one with the uncommonly reported EWSR1-FEV translocation

Aims: Primary Ewing sarcoma of the ileum has rarely been documented. Little is known about its pathogenesis and clinical implications, and it would be helpful to identify novel molecular markers. EWSR1-FEV translocation is exceedingly rare in Ewing sarcoma, as FEV expression is restricted to prostate, brain and serotonin neuroendocrine cells (NE) and related tumours. Methods and Results: Paraffin sections or snap-frozen material were used in this investigation. Tumours were investigated by means of immunohistochemistry, RT-PCR (EWSR1-FLI1, EWSR1-ERG and EWSR1-FEV transcripts), FISH analysis (EWSR1 break-apart and specific EWSR1-FEV translocation) and spectral karyotyping (SKY). Ten ileal neuroendocrine tumours (INET) made up the control group for EWSR1-FEV translocation. Among 445 Ewing sarcomas cases spanning a period of 20 years, seven (1.6%) arose in the ileum. All tumours were immunoreactive for synaptophysin, CD99, FLI1 and vimentin. FISH identified EWSR1 rearrangement in all cases, with EWSR1-FLI1 transcripts being detected in all but one tumour showing the uncommon EWSR1-FEV rearrangement, with SKY, RT-PCR and FISH confirmation. The mean survival of EWSR1-FLI1 patients was 14 months, whereas the EWSR1-FEV patient was alive after 15 years despite several recurrences controlled by surgery alone. No INET showed EWSR1 translocation. Conclusions: Most primary Ewing sarcomas of the ileum show the common EWSR1-FLI1 translocation, but EWSR1-FEV could be specific for tumours arising in the ileum and showing better prognosis.