Primitive neuroectodermal tumors of bone and soft tissue. With reference to histologic differentiation in primary or metastatic foci.

Primitive neuroectodermal tumors (PNET) of the bone and soft tissue were reviewed by immunohistochemistry and partly by morphometry, focusing particularly on histologic changes in recurrent or metastatic foci, in order to elucidate their probable histogenetic relationship with Ewing's sarcoma (ES) and its extraskeletal counterpart (EES). Eleven cases of bone tumor (average patient age; 15.1 yr) and 12 cases of soft tissue tumor (average patient age; 22.1 yr) which disclosed unequivocal Homer-Wright rosettes and/or at least foci of ganglion cell differentiation either in a given primary tumor or metastatic (or recurrent) foci were selected from small round cell tumors primarily categorized as ES or EES. Most of the cases for which follow-up biopsy samples were available disclosed prominent Homer-Wright rosettes in the metastases, whereas the primary tumors showed features of ES and lacked rosettes. In only one case, Homer-Wright rosettes were absent in the metastatic tumor. Most cases had been treated by combined intensive chemotherapy and radiotherapy, which might have influenced cell differentiation. Neural markers (neuron-specific enolase, neurofilament protein and others) were positive in most cases. Three cases with otherwise typical histologic features of ES or EES showed minute foci of ganglion cell differentiation, as confirmed by morphometry and neural markers. These results suggest that ES (or EES) and PNET are histogenetically related, but represent different stages of cell differentiation.