Round Cell Pattern

•  ES/PNET

•  Alv RMS

•  DSRCT

•  Neuroblastoma

•  Small cell/Merkel cell

•  Lymphoma

•  Mesenchymal CS

•  Round cell LS

•  Poorly diff SS

•  “Ewing-like”

•  CIC-DUX

•  BCOR-CCNB3

•  CIC-FOXO4

PAS/D

ES/PNET: Histologic Spectrum

ES PNET

Cell shape regular irregular

Chromatin fine coarse

Nucleoli pinpoint prominent

Glycogen abundant scant

Rosettes absent present

ES/PNET: Ultrastructure

ES/PNET: Ultrastructural Spectrum

Feature ES PNET

Organelles scarce abundant

Dense-core granules absent abundant

Neurotubules absent abundant

Neuritic processes absent abundant

CD99

MIC - 2 Gene Product (CD99)

Diagnosis Positive (%)

ES/PNET 93%

Small Cell Osteosarcoma 12%

Desmoplastic Round Cell Tumor 20%

Neuroblastoma 0%

Rhabdomyosarcoma 15%

Small Cell Carcinoma 9%

T-LL/ALL 92%

ES/PNET: Cytogenetics

t(11;22)(q24;q12) – FLI1;EWSR1 Translocation

EWSR1 FLI1

NH2 COOH

ETS DNA binding domain

t(21;22)(q22;q12) ERG/EWSR1

t(7;22)(p22;q12) ETV1/EWSR1

t(17;22)(q12;q12) FEV/EWSR1

t(2;22)(q33;q12) E1AF/EWSR1

Very rare involvement of FUS in lieu of EWSR1

EWSR1 (22q12) Break-apart probe

t(11;22), t(21;22) – EWSR1/PNET (FLI1/EWSR1, ERG/EWSR1)

t(11;22) - DSRCT (WT-1/EWSR1)

t(12;22) – Clear Cell Sarcoma (ATF1/EWSR1)

t(9;22) – ES Myxoid Chondrosarcoma (NR4A3/EWSR1)

t(12;22) – Myxoid/Round Cell Liposarcoma (DDIT3/EWSR1)

t(2;22) – Angiomatoid fibrous histiocytoma (CREB1/EWSR1)

t(6;22) – Soft tissue myoepithelioma (Pou5F1/EWSR1)

Rhabdomyosarcoma International Classification

Favorable Prognosis

• Botryoid

•  Spindle cell

Intermediate Prognosis

•  Embryonal

Poor Prognosis

• Alveolar

Newton WA et al, Cancer 1995

MyoD1/Myogenin

•  part of the Myo-D superfamily of genes

•  encode for DNA binding proteins which

activate transcription of skeletal muscle-

specific genes

•  results in commitment to skeletal muscle

differentiation

•  can detect skeletal muscle differentiation

at an earlier stage than with markers

currently available Myogenin

Myogenin in Pediatric Tumors

Tumor Cases stained

Rhabdomyosarcoma (69) 69/69 (100%)

•  Alveolar (48)

•  Embryonal (20)

•  Spindle cell (1)

Other pediatric sarcomas (50) 0/50 (0%)

•  ES/PNET (16)

•  DSRCT (6)

•  Neuroblastoma (4)

•  Others (24)

Kumar S et al, Mod Pathol 2000

Alveolar Rhabdomyosarcoma

t(2;13)(q35;q14) t(1;13)(q36;q14)

PAX3/FOXO1A PAX7/FOXO1A

*up to 25% lack t(2;13) or t(1;13)

FOXO1A Break Apart Probe

“Ewing-like” Sarcoma

CIC-DUX BCOR-CCNB3

CIC-FOXO4

•  Lobular growth

•  Geographic necrosis

•  Round cells

•  High-grade nuclei

•  Patchy clear cytoplasm

•  Foci of myxoid change

CIC-DUX Sarcomas

CIC-DUX Sarcomas

Immunophenotype

S-100 protein negative

TLE1 negative

Desmin negative

Myogenin negative

WT1 positive

INI1 retained

CIC-DUX Sarcomas

Immunophenotype

CD99 7/7

(focal 5/7; cytoplasmic, not membranous)

ERG 9/10

FLI1 8/8

Choi et al. AJSP 2013

Smith et al. Mod Pathol 2014

CIC-DUX Sarcomas

Other Findings

•  t(4;19) 8/10

•  t(10;19) 2/10

•  Trisomy 8 3/3

•  MYC staining 10/10 (diffuse)

•  MYC amplification (FISH) 6/7

Smith et al. Mod Pathol 2014

CIC-DUX Sarcomas

Clinical Outcome (N=13)

•  Died of disease 8 (9-17 mos; mean: 12 mos)

•  Alive with disease 1 (24 mos)

•  No evidence of disease 4 (6-30 mos)

•  Metastases: Lung (10); Brain (2); Pelvis (2); Bone (1)

BCOR-CCNB3 Sarcomas

•  Gender: 9M / 1F

•  Age: 11-18 yrs

•  Location: 7 bone / 3 deep soft tissue

•  Follow-up: 5-189 mos (median: 695 mos)

•  AWOD 6/10

•  AW mets 1/10

•  DOD 3/10

Puls et al AJSP 2014

BCOR-CCNB3 Sarcoma •  Morphology

•  Round cell resembling atypical Ewing sarcoma : 7 cases

•  Spindle cell sarcoma: 3 cases

•  Immunophenotype

•  CCNB3 10/10

•  bcl2 9/10

•  CD99 7/10

•  CD117 6/10

•  Desmin 0/10

•  AE1/3 0/3

•  RT-PCR: 9/9 BCOR-CCNB3 fusion

Puls et al AJSP 2014

BCOR-CCNB3 CCNB3 stain

Courtesy of Dr. Florian Puls

BCOR-CCNB3 CCNB3 stain

Courtesy of Dr. Florian Puls

Round Cell Pattern CD99 TdT Myo Cam 5.2 Des WT1

ES/PNET + - - 20% - -

A-RMS 15% - + 50% + -

Lymphoma >90% + - - - -

DSRCT 20% - - + + +

CIC-DUX + (focal) - - - - +