ENO2 and Ewing sarcoma: These include neuron-specific enolase (NSE) and GD2, which are present in NB and sometimes in osteosarcomas and rhabdomyosarcomas;2,3 CD99 expressed by Ewing's sarcoma and by some PNETs;4,5 NB84 expressed by NB cells and sporadically by Ewing's and PNETs;6 and desmin and cytokeratin present in desmoplastic tumours.7 However, none of these markers has, by itself, clinical utility in unambiguously differentiating small round blue cell tumours.8