29
Pediatric Tumors
Table 29.2 Differential Diagnosis of Malignant Round Cell Tumors in Children
Neoplasm type
Age group
Location
Cytologic features
Immunopositivity
Electron
microscopy
Genetic
disorders
Neuroblastoma
< 5 years
Adrenal gland,
sympathetic gan-
glion, and other
sites of the neural
crest
Dispersed small cells
with small to medium-
sized nuclei and scanty
cytoplasm; occasionally
rosettes, scattered large
neuroblasts, ganglion cells,
and neurofibrils
NSE, neurofila-
ments, peripherin,
chromogramin,
synaptophysin, TrK
receptor protein
Neurites and
neurosecretory
granules
Loss of distal
region of
short arm of
chromosome 1,
amplification of
N-myc oncogene
Lymphoblastic
lymphoma
Diverse
Thymic region
Cells with lobulated or
convoluted nuclei and
inconspicuous nucleoli
T-cell markers: CD1,
CD2, CD7, CD43,
and CD71
Cerebroid nuclei
Translocations
of the alpha
and delta T-cell
receptor loci at
14q 11.2, beta
locus at 7q35,
and gamma
locus at 7p14-15
Burkitt's
lymphoma
< 5 years
Sporadic: abdomi-
nal cavity
Endemic:
jaws and orbit
Cytoplasmic vacuoles, two
to five distinct nucleoli, tin-
gible body macrophages
B-cell markers:
CD10, CD19, CD20,
CD22, CD24,
HLA-DR, and im-
munoglobulins,
especially IgM
Cytoplasmic
vacuoles
t(8;14)(q23;q21)
translocation
Wilms' tumor
< 5 years
Abdomen and
kidneys
Multiple patterns:
rounded, spindle, and
epithelial cells
Blastemal cells:
vimentin, NSE,
desmin, and cyto-
keratin
Neural cells: S-100
protein, GFAP, and
NSE. Mesenchyma-
tous cells: desmin,
myogenin, and
NSE
Cells like those of
metanephros
WT1 gene, WT2
gene
Primitive neu-
roectodermal
tumor-Ewing's
sarcoma
> 10 years
Bones or soft
tissues
Dyscohesive rounded
cells and occasionally
Homer-Wright rosettes
CD99, vimentin,
low molecular
weight keratins,
NSE, protein
product 9.5, Leu7,
neurofilaments
Few specialized
junctions
Reciprocal
translocation
11,12(q24, q 12),
deletion of
INKA4A
Alveolar rhabdo-
myosarcoma
> 10 years
Soft tissues of
head, neck, and
extremities
Occasionally cells forming
alveolar structures and
nests
Myosin, sarcomeric
actin, myoglobin,
and vimentin
Intermediate
filaments
t(2,13)(q35, q14)
translocation,
t(1, 13)(q36, q14)
translocation,
gene fusion
PAX3-FKHR,
gene fusion
pAX7-FKHR
Embryonary
rhabdomyo-
sarcoma
< 5 years
Soft tissues of
head, neck,
extremities, and
urogenital tract
Occasionally large rhab-
domyoblastic and multi-
nucleated cells with strap
shape and cytoplasmic
cross-striations
Actin and desmin
Sarcomere-related
structures, lepto-
meric structures
t(2,13)t(1,13)
translocation
Desmoplastic
round cell
tumor
> 10 years
Abdominal, perito-
neum and pelvis
Dispersed small undiffer-
entiated cells
proteins associated
with epithelial,
muscular, and neu-
ral differentiation:
cytokeratins, epi-
thelial membrane
antigen, desmin,
NSE
Few specialized
junctions
Gene fusions,
WT1-EWS,
t(11,22)(p13,q12)
translocation
Continued
947
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