There are two reasons for this: firstly, morphologically and biologically such tumours are all similar and are characterised by the presence of the Fli-l;EWS fusion gene (Parham, 1996) and secondly, even with full clinical information it is often difficult to determine the origin of such tumours and not possible to ascertain whether a tumour is arising in bone and invading soft tissue or vice versa. The gene discussed is EWSR1; the disease is neoplasm.