Acute Undifferentiated Leukemia Presented With Mediastinal Sarcoma.

Acute undifferentiated leukemia (AUL) is a rare, aggressive type of acute leukemia associated with poor prognosis, in which the blasts lack lineage commitment to either the myeloid or lymphoid lineages. It is classified according to the World Health Organization (WHO) classification under the category of acute leukemias of ambiguous lineage (ALAL). Here we present a case of a 20-year-old man, who was referred to Military Cancer Center in February 2025, as a case of mediastinal myeloid sarcoma, which was diagnosed by biopsy of the mass. Bone marrow examination was performed in our center and showed infiltration by blasts, flow cytometry of bone marrow aspirate specimen revealed that blasts do not express lineage-specific markers with expression of primitive markers, so the diagnosis of AUL was established. For precise diagnosis of AUL, a comprehensive and broad panel of immunomarkers should be run to rule out any lineage commitment for the clone. Review of literature revealed only one previously published similar case.