Granulocytic sarcoma masquerading as Ewing's sarcoma: a diagnostic dilemma.

An eleven-year-old boy presented with a swelling in his left elbow. Radiologically the features were that of an Ewing's sarcoma involving the ulna. Histopathology showed small round cell tumor strongly positive for Monoclonal Imperial Cancer research fund 2 (MIC2) antigen. Similar cells in the bone marrow were involved with MIC2 positivity. The patient developed skin lesions, which on biopsy were found to be chloromas. The initial biopsies were reevaluated with special stains revealing granulocytic sarcomas in acute myeloid leukemia masquerading as Ewing's due to its MIC2 positivity. The possibility of myeloid neoplasms should be considered routinely with known MIC2 positive round cell tumors.