Leukemia - Acute - Microgranular variant of acute promyelocytic leukemia

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Leukemia - Acute

AML with recurrent genetic abnormalities

Microgranular variant of acute promyelocytic leukemia

Reviewer: Syed Zaidi, M.D. (see Reviewers page)
Revised: 20 February 2013, last major update September 2012
Copyright: (c) 2001-2013, PathologyOutlines.com, Inc.

General
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● Formerly called AML-M3v
● Note: “variant” APL without further description may mean microgranular variant or an APL variant other than t(15;17)
● Peripheral blood white blood count usually elevated, in contrast to hypergranular form
● Diagnosis: cytogenetics recommended because other AML cases may appear similar (Am J Clin Pathol 2002;117:651)

Prognostic factors
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● Treatment with ATRA and anthracyclines recommended for APL
● CD56 expression associated with less favorable prognosis

Case reports
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● 5 year old girl with Down’s syndrome (J Med Case Rep 2007;1:147)
● 69 year old woman post-chemotherapy for breast cancer (Cancer Genet Cytogenet 2002;138:143)
● Nine years after diagnosis of essential thrombocythemia (Am J Hematol 2002;71:114)

Micro description
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● Predominatly bilobed leukemic cells have fewer and smaller cytoplasmic granules, usually multiple Auer rods but less than classic (hypergranular) promyelocytic leukemia
● Nuclei is folded, convoluted and markedly irregular

Micro images
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Promyelocytes have abundant fine azurophilic cytoplasm with
variable size and basophilia, markedly lobulated and invaginated nuclei

Small hyperbasophilic promyelocytes with prominent cytoplasmic
budding, most cells have sparsely granular cytoplasm and lobulated nuclei

Positive stains
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● Usually CD2 (Leukemia 1995;9:1461), CD13, CD33, CD34 (relatively more common than hypergranular variant, Haematologica 2006;91:311) and myeloperoxidase (strong)

Molecular description
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● Associated with FLT-3-ITD mutations (Br J Haematol 2004;125:463) and different gene expression profiles than hypergranular APL (Genes Chromosomes Cancer 2005;43:113)

Variant translocatios in acute promyelocytic leukemia:
● A subset of cases which morphologically resemble APL and show variant translocation involving the RARA
● Fusion partners include:
     ● ZBTB16 (previously known as PZLF) on 11q23
     ● NUMA1 (nuclear matrix associated gene1) on 11q13
     ● NPM1 (nucleophosmin gene) at 5q35
     ● STAT5B at 17q11.2

Electron microscopy description
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● Stellate array of endoplasmic reticulum is characteristic

Electron microscopy images
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Smaller granules than hypergranular variant, granules are more uniform in size and endoplasmic reticulum is prominent

Small granules and stellate array of endoplasmic reticulum

Differential diagnosis
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● Other AML: see Am J Clin Pathol 2002;117:651

End of Leukemia - Acute > AML with recurrent genetic abnormalities > Microgranular variant of acute promyelocytic leukemia

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