De novo myeloid sarcoma in a 4-month-old infant: a case report and review of the literature.

Myeloid sarcoma is a rare tumor of immature myeloid cells in an extramedullary site. Myeloid sarcoma may present in a variety of locations; skin is one of the common sites. It may precede or occur concurrently with acute myeloid leukemia, chronic myeloid leukemia, other forms of myeloproliferative disorders/myelodysplastic syndrome or de novo. We report a case of a 4-month-old female who presented with cutaneous lesions without evidence of leukemia, determined to be de novo myeloid sarcoma. She had erythematous nodules in multiple skin sites. Biopsy revealed a diffuse atypical mononuclear cell infiltrate involving the entire dermis and extending to the subcutis. The infiltrate was diffusely positive for lysozyme, CD43, CD15, CD33, CD68 and CD117 and was negative for CD3, CD20, CD34, CD56, CD79a, CD99, myeloperoxidase, desmin, chromogranin and synaptophysin, supporting a diagnosis of myeloid sarcoma. No leukemic involvement was found on evaluation of peripheral blood or bone marrow aspiration. Chromosomal abnormalities were found at chromosomes 7, 10 and 11. The skin lesions resolved following multiple chemotherapy courses, then recurred requiring additional treatment. De novo myeloid sarcoma involving skin without evidence of leukemia can occur in an infant and may present a diagnostic challenge.