AML with t(1;22)(p13;q13)

Epidemiology and Etiology:

· infants and young children (3 y or less) (median 4 months)

· not Down syndrome

· F > M

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Common sites:

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Gross features:

· Marked organomegaly

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Histologic features:

· maturation in the megakaryocyte lineage

· Similar to acute megakaryoblastic leukemia of AML, NOS

· Small and large megakaryoblasts maybe

· Basophilic agranular cytoplasm

· Blebbing or pseudopod formation maybe

· Morphologically undifferentiated blasts resembling lymphoblasts maybe

· Micromegakaryocytes common

· No dysplastic erythroid or granulocytic features usually

· Straomal pattern of BM infiltration mimicking a metastatic tumour maybe

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Immunophenotype:

Marker:

Sensitivity:

Specificity:

• Negative in megakaryoblasts: sudan black B (SBB), MPO
• Positive in megakaryoblasts: one or more of the platelet glycoproteins: CD41, CD61, maybe CD42 (cytoplasmic more specific than membranous); CD36
• Maybe in megakaryoblasts: CD13, CD33
• Often neg in megakaryoblasts: CD34, CD45, HLA-DR
• Negative in megakaryoblasts: lymphoid markers, TdT

Molecular features:

· RNA-binding motif protein-15 (RBM15 aka OTT)

· Megakaryoctye leukemia-1 (MKL1 aka MAL)

· Fusion gene may modulate chromatin organization, HOX-induced differentiation, and extracellular signaling pathways

· Associated karytotypic abnormalities:

· Usually sole karyotypic abnormality

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Other features:

· Early reports suggested a poor prognosis

· More recent studies find good response to intensive AML chemotherapy

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References:

· Swerdlow. WHO Classification of Tumours of Haematopoietic and Lymphoid Tissue. 4th ed. WHO Publications; 2008.

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