Isolated mediastinal myeloid sarcoma after NPM1-positive pediatric acute myeloid leukemia

Myeloid sarcoma (MS) is a rare extramedullary mass that consists of immature myeloid cells. The most common locations are the soft tissue, bone, periosteum, orbit, and lymph nodes [1,2]. Mediastinal involvement is very rare and most commonly reported with concurrent bone marrow involvement [3]. Herein we present a previously treated nucleophosmin (NPM1)-positive acute myeloid leukemia (AML) patient who later presented with isolated mediastinal MS.