Frequently occurred at diaphysis of long bones of 2nd and 3rd decades. The tumor is composed by diffuse proliferation of monotonous small round cells. Tumor with Homer-Wright rosettes, differentiation towards to ganglion cells, and neuroendocrine granules is called as primitive neuroectodermal tumor (PNET), and distinguished. However, it is the same tumor of different differentiation. As shown in the figure above, chromosomal reciprocal translocation (t(11;22)), mutation gene (EWS/Fil1) or its subtype are sometimes seen.

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