Answer
Acute undifferentiated leukemia (AUL) is extremely rare, and little is known about the frequency of this disease.
Mixed phenotype acute leukemia (MPAL) with t(9;22)(q34;q11.2) (or BCR-ABL1 rearrangement) is also rare, accounting for less than 1% of acute leukemias. It is the most common form of MPAL that is associated with a recurrent cytogenetic abnormality. This diagnosis should not be made in patients with known chronic myeloid/myelogenous leukemia (CML) who progress to the blast phase with features of MPAL. Although this condition does occur in children, it is more common in adults.
MPAL with t(v;11q23) (or KMT2A (MLL) rearrangement) is more common in children and infants than older individuals. The MPALs (B/myeloid and T/myeloid types) include those that are biphenotypic or of mixed lineage. They account for less than 1% of acute leukemias.
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Pathology of Acute Leukemias of Ambiguous Lineage. Blasts of acute undifferentiated leukemia.
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Pathology of Acute Leukemias of Ambiguous Lineage. Blasts of mixed phenotype acute leukemia with t(4;11q23).
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Pathology of Acute Leukemias of Ambiguous Lineage. Blasts of acute myeloid leukemia, type M0.
