Test Details: The Ewing's family of tumours (EFTs) are characterized by chimeric transcripts generated by specific chromosomal rearrangements. The most common fusions are between the EWSR1 gene on chromosome 22 and the ETS family of transcription factors. There are different types of EWSR1-FLI1 fusion transcripts resulting from translocation t(11;22), three types of EWSR1-ERG transcripts resulting from t(21;22) and one type of t(2;22) resulting in EWSR1-FEV fusion. FISH (Fluorescence In Situ Hybridization) is used to validate the diagnosis of EFT (as opposed to other small round cell tumours) where the gene rearrangement involved in a translocation is determined.