The neuroectodermal tumor of bone.

Four small round cell malignant tumors of bone occurring in children are described. There was no catecholamine secretion and the clinical, radiologic, and biopsy diagnosis in each was Ewing's sarcoma. Glycogen was sparse both on imprints and in tissue sections. The tumors, when extensively sampled, had areas of a lobular growth pattern and Homer Wright rosettes. The rosettes were always focal and varied in complexity from case to case; they were rudimentary in one instance and markedly fibrillar in the most obvious instance. Neuron-specific enolase was demonstrated in tissue sections and in longterm cell cultures from three of the tumors. The cultured cells put out moderately long beaded processes in serum-free medium but had no catecholamine fluorescence. Electron microscopy of the tumor rosettes and the cultured cells showed processes containing aggregates of microtubules and only one case had rare neurosecretory granules. This study suggests that some small round cell tumors of bone and soft tissue in children, which present as Ewing's sarcoma, are neuroectodermal in nature.