Myeloid Sarcoma with a PICALM–MLLT10 Fusion Presenting as an Isolated Mediastinal Mass in a Middle-Aged Asian Male: A Case Report

Myeloid sarcoma (MS), also known as granulocytic sarcoma or chloroma, is a rare extramedullary manifestation of acute myeloid leukemia (AML). Mediastinal presentation is exceedingly uncommon and may lead to misdiagnosis, particularly when hematologic parameters are preserved. We report the case of a 44-year-old male who presented with constitutional symptoms and an isolated anterior mediastinal mass without peripheral blood abnormalities. Diagnosis was established through flow cytometry, histopathology, and immunohistochemistry. Molecular profiling revealed a complex mutational landscape including PHF6, TP53, WT1 mutations, and a PICALM–MLLT10 fusion. The patient was treated with AML-directed chemotherapy and remains under close surveillance. This case highlights the diagnostic challenges and prognostic implications of extramedullary AML with rare genetic alterations.