Mediastinal myeloid sarcoma

Abstract Myeloid Sarcoma is a rare tumor mass composed of immature myeloid cells that can affect any anatomical structure and is often misdiagnosed as non-Hodgkin lymphoma. We present the case of a 14-year-old female patient who initially presented with pleural effusion and a mediastinal mass. Her diagnosis involved three different healthcare institutions and required an integrated approach including biopsy, cytology, flow cytometry, and clinical evaluation. She was initially diagnosed with B-cell lymphoblastic lymphoma at Hospital A, then reclassified as T-cell lymphoblastic lymphoma at Hospital B. Due to unfavorable clinical progression, she was admitted to Hospital C, where a review of biopsy slides, immunohistochemistry, and flow cytometry FCS files from the previous centers was performed. Further immunohistochemical studies led to the reclassification of the neoplasm as Myeloid Sarcoma. The case was sent abroad for confirmation and was diagnosed as Mediastinal Granulocytic Sarcoma with PICALM:MLLT10 fusion. The patient was first treated with the Total XV protocol, and after the diagnosis change at Hospital C, treatment was switched to the ADE protocol. The expression of markers such as MPO and CD34 in flow cytometry and immunohistochemistry was crucial for establishing the differential diagnosis.