Molecular variants of the EWS-WT1 gene fusion in desmoplastic small round cell tumor.

We report two cases of desmoplastic small round cell tumor (DSRCT) with novel molecular variants of the specific EWS-WT1 gene fusion. This fusion usually encodes a chimeric RNA with an in-frame junction of exon 7 of EWS to exon 8 of WT1. In one variant patient, the EWS-WT1 fusion transcript contained an in-frame junction of exon 9 of EWS to exon 8 of WT1. Moreover, in this patient the tumor arose in the hand, an extremely unusual site for DSRCT. In the second patient, an in-frame junction of exon 10 of EWS to exon 8 of WT1 was present. These two cases of DSRCT show that the molecular variability in the EWS breakpoint observed in the EWS-FLI1 fusion of Ewing's sarcoma can occur in DSRCT as well. This type of heterogeneity is relevant to the interpretation of molecular diagnostic assays and could also affect the functional properties of the encoded chimeric transcription factors.