Transient abnormal myelopoiesis (TAM) in Down Syndrome

Epidemiology and Etiology:

· Down syndrome newborns (10% of DS newborns)

· Trisomy 21 mosaics (may be phenotypically normal)

· Clinical and morphologic findings indistinguishable from AML

· Spontaneous remission within the first 3 months of life

Common sites:

·

Gross features:

· Hepatosplenomegaly maybe

Cytologic features:

· Morphology similar to most cases of DS AML

· Blasts with basophilic cytoplasm

· Coarse basophilic granules

· Cytoplasmic blebbing suggestive of megakaryoblasts

Immunophenotype:

· immunophenotype similar to most cases of DS AML

Marker:	Sensitivity:	Specificity:
CD34
CD56
CD117
CD13
CD33
CD7
CD4 (dim)
CD41
CD42
TPO-R
IL-3R
CD36
CD61
CD71
HLA-DR	30%
MPO (neg)
CD15 (neg)
CD14 (neg)
Glycophorin A (neg)

Molecular features:

· cytogenetics:

· trisomy 21 (constitutional)

Other features:

· Blood counts:

· Thrombocytopenia

· Other cytopenias less frequent

· Marked leukocytosis maybe

· Blast percentage in PB may exceed that in BM

· Basophilia in some

·

References:

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