Nucleolar organizer regions in small cell tumours of childhood.

A silver colloid technique for nucleolar organizer regions (AgNORs) was applied to paraffin sections of 50 small cell tumours of childhood. These comprised 20 neuroblastomas, 10 Ewing's sarcoma, and 20 rhabdomyosarcomas, including spindle cell, myxoid, and round cell variants. On the basis of the number of AgNORs, one could differentiate between the three groups. The differences observed were statistically significant (P = 0.01-0.001). The subtypes of rhabdomyosarcoma could not be distinguished from one another on the basis of AgNOR counts. We suggest that this simple histochemical technique may be a useful adjunct to the range of special techniques now available to assist the pathologist in the diagnosis of small round cell tumours.