Acute undifferentiated leukemia Mixed phenotype acute leukemia with t(9;22)(q34.1;q11.2); BCR-ABL1 Mixed phenotype acute leukemia with t(v;11q23.3); KMT2A rearranged Mixed phenotype acute leukemia, B/myeloid, NOS Mixed phenotype acute leukemia, T/myeloid, NOS

• Myeloid: MPO (+)
• T-ALL: CD3 (+)
• B-ALL: some can be CD19-
• CD117-: basophilic leukemia
• CD117+: mast cell leukemia
• The WHO definition of MPAL does not separate cases with a single blast cell population showing a mixed phenotype (biphenotypic) from cases with two distinct blast cell populations (bilineal) because there is great overlap between these case types with some presenting with one pattern and relapsing with another.

• Available data suggest that these patients may benefit from ALL rather than AML treatment regimens.