Malignant round cell tumor of bone with neural differentiation (neuroectodermal tumor).

A malignant round cell tumor primary in bone is reported in a young girl, showing histologically rosette formation and pseudoalveolar spaces. Vimentin, NSE, and S-100 were positive. Electron microscopy demonstrated abundant glycogen and neural features such as cell processes, microtubules, and occasional dense-core granules. Whether this neuroectodermal tumor represents a separate entity or is a variant of Ewing's sarcoma should wait for further experience, in the light of recent evidence suggesting that Ewing's sarcoma arises from primitive multipotential cells.