Cutaneous extraskeletal Ewing's sarcoma.

Extraskeletal Ewing's sarcoma has been recognized as being histologically indistinguishable from Ewing's sarcoma of bone. Although the occurrence of extraosseous Ewing's sarcoma in deep soft tissues has been well described, such cutaneous lesions are rare. We report the clinical history, histopathologic findings, and results of ultrastructural study of this rare variant occurring in a 12-year-old girl. She presented with a dermal and subcutaneous tumor of the left third toe, without osseous involvement. The lesion was composed of masses of round-oval cells, with perilobular fibrosis, focal hemorrhage, ill-defined pale cytoplasm containing glycogen, and absent pericellular reticulin. Ultrastructural study showed a monotonous cell population, with focal thickening of apposing membranes, high nuclear/cytoplasmic ratio, copious intracytoplasmic glycogen, and paucity of organelles except mitochondria. We present this case along with discussion of the literature and problems concerning differential diagnosis of small cell malignancies in the skin.