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Bone marrow involvement by Ewing sarcoma is characterized on aspirate smears by a monotonous population of small round blue cells. These tumor cells show a high nuclear-to-cytoplasmic ratio, with scanty, faintly eosinophilic to basophilic cytoplasm few with small cytoplasmic blebs, often containing glycogen vacuoles. The nuclei are round with finely dispersed (“stippled”) chromatin and small, inconspicuous nucleoli.