A Rare Case of Relapsed Pediatric Acute Promyelocytic Leukemia with Skin Involvement by Myeloid Sarcoma.

BACKGROUND Acute promyelocytic leukemia (APL) is a very rare leukemia in children. Extramedullary involvement by APL has been reported in between 3-5% of cases, mainly associated with cases of relapse. A rare case of relapse of APL in a 9-year-old child is presented with skin involvement with myeloid sarcoma. CASE REPORT A 9-year-old male child was admitted to the Oncology Service of the hospital complaining of fever, progressive fatigue, oral petechiae with severe bleeding in the oral cavity. Bone marrow examination showed some promyelocytes. Flow cytometry showed 86% immature myeloid cells with the t(15;17) translocation, and molecular analysis showed expression of the PML/RARa fusion protein, which confirmed the diagnosis of APL. The patient completed a course of daunorubicin, cytarabine, and AII trans-retinoic acid (ATRA) with complete remission. After six months, the patient was re-admitted to hospital with a violaceous lesion on the scalp, with relapse of APL. Histological and immunohistochemistry of the lesion involving the skin of the scalp showed a myeloid sarcoma invading the dermis. CONCLUSIONS Myeloid sarcoma, also called granulocytic sarcoma, is an extramedullary tumor of immature myeloid cells, which very rarely presents in children with APL. The mechanisms that lead to myeloid sarcoma in children with APL and the possible association with ATRA therapy remain to be investigated.