Leukemia - Acute - Mixed phenotype acute leukemia

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Leukemia - Acute

Other ALL

Mixed phenotype acute leukemia (MPAL)

Reviewer: Daniela Mihova, M.D. (see Reviewers page)
Revised: 28 September 2012, last major update September 2012
Copyright: (c) 2001-2012, PathologyOutlines.com, Inc.

General
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● De novo acute leukemia containing separate populations of blasts of more than one lineage (bilineal or bilineage), or a single population of blasts co-expressing antigens of more than one lineage (biphenotypic)

Excludes:
● Acute myeloid leukemia (AML) with recurrent translocations t(8;21), t(15;17) or inv(16)
● Leukemias with FGFR1 mutations
● Chronic myelogenous leukemia (CML) in blast crisis
● Myelodysplastic syndrome (MDS)-related AML and therapy-related AML, even if they have MPAL immunophenotype

Criteria for biphenotypic leukemia:
● Score of 2 or more for each of two separate lineages:

The European Group for the Immunological Classification of Leukemias (EGIL) scoring system

2008 WHO classification of acute leukemias of ambiguous lineage

Prognosis
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● Poor, overall survival of 18 months
● Young age, normal karyotype and ALL induction therapy are associated with favorable survival
● Ph+ is a predictor for poor prognosis
● Bone marrow transplantation should be considered in first remission

Major Categories

MPAL with t(9;22)(q34;q11.2); BCR-ABL1
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● 20% of all MPAL
● Blasts with t(9;22)(q34;q11.2) translocation or BCR-ABL1 rearrangement (Ph+) without history of CML
● Majority in adults
● High WBC counts

● Most of the cases B/myeloid phenotype
● Rare T/myeloid, B and T lineage, or trilineage leukemias

Morphology:
● Many cases show a dimorphic blast population, one resembling myeloblasts and the other lymphoblasts

Cytogenetic abnormalities:
● Conventional karyotyping for t(9;22), FISH or PCR for BCR-ABL1 translocation
● Additional complex karyotypes
● Ph+ is a poor prognostic factor for MPAL, with a reported median survival of 8 months
● Worse than patients of all other types of MPAL

MPAL with t(v;11q23); MLL rearranged
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● Meeting the diagnostic criteria for MPAL with blasts bearing a translocation involving the 11q23 breakpoint (MLL gene)
● MPAL with MLL rearranged rare
● More often seen in children and relatively common in infancy
● High WBC counts
● Poor prognosis
● Dimorphic blast population, with one resembling monoblasts and the other resembling lymphoblasts
● Lymphoblast population often shows a CD19+, CD10- B precursor immunophenotype, frequently CD15+
● Expression of other B markers usually weak
● Translocations involving MLL gene include t(4;11)(q21;q23), t(11;19)(q23;p13), and t(9;11)(p22;q23)
● Cases with chromosome 11q23 deletion should not be classified in this category

Cytogenetics images:

t(4;11)(q21;23) in bilineal leukemia

MPAL B/Myeloid, NOS
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● Meets the diagnostic criteria for MPAL with both B and myeloid lineages without Ph+ and MLL rearrangement
● B/myeloid acute leukemia accounts for 1% of all leukemias
● More common in adults, but also seen in children

Morphology:
● Dimorphic populations, resembling lymphoblasts and myeloblasts, or a single population resembling ALL

Genetics:
● Multiple different cytogenetic changes have been demonstrated, however none is proven to be specific in this subtype

MPAL T/Myeloid, NOS
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● Meets the diagnostic criteria for MPAL with both T and myeloid lineages without Ph+ and MLL rearrangement
● More often in children, though in adults as well
● Dimorphic populations, resembling lymphoblasts and myeloblasts, or a single population resembling ALL
● Other commonly expressed T-lineage markers include CD2, CD7
● Myeloid markers MPO, CD117, TdT, CD13 and CD33
● T cell plus myeloid cases may have 2p13 translocations or other unrelated anomalies (Leukemia 2007;21:2264)

End of Leukemia - Acute > Other ALL > Mixed phenotype acute leukemia

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