Extrarenal Rhabdoid Tumor

Differential Diagnosis

Carcinomas may mimic extrarenal rhabdoid tumors and in rare cases be morphologically indistinguishable

The following features favor carcinoma
- Age over 50 years
- Areas exhibiting cohesive epithelial differentiation
- History of carcinoma
Identification of abnormalities of the long arm of chromosome 22 supports rhabdoid tumor

Melanomas may mimic extrarenal rhabdoid tumors and in rare cases be morphologically indistinguishable

Any of the following features of melanoma rule out a diagnosis of rhabdoid tumor
- History of melanoma
- S100 or HMB45 reactivity
- Keratin negativity
Identification of abnormalities of the long arm of chromosome 22 supports rhabdoid tumor

Anaplastic Large Cell Lymphoma	Extrarenal Rhabdoid Tumor
LCA and or T lineage markers positive	LCA and T lineage markers negative
Keratin rare, faint	Keratin 100% positive
CD30, ALK positive	No data available for CD30, ALK
INI1 expressed 100% (few tested)	INI1 loss 85%
Translocation of chromosome 2 short arm	Various deletions, translocations involving 22q11

LCA and T lineage markers are occasionally undetectable in ALCL

Extrarenal Rhabdoid Tumor	Proximal Type Epithelioid Sarcoma
CD34 negative	CD34 50% positive
No intensely eosinophilic collagen	Intensely eosinophilic collagen
Median age 8-9 years	Median age 35-40 years
Wide range of sites	Predilection for genitalia

It is probable that malignant rhabdoid tumors do not occur in adults - most if not all are carcinoma, melanoma or proximal epithelioid sarcoma

Rhabdomyosarcoma	Extrarenal Rhabdoid Tumor
Desmin, actin, myoglobin or MyoD1 positive	Muscle markers negative (definitional)
Keratin 5-50% positive, focal, weak	Keratin 100% (definitional)
INI1 expression retained 100%	INI1 loss 85% nearly definitional
May have cross striations	No cross striations
May have strap cells	Strap cells rare
No consistent abnormalities of 22q	Various deletions, translocations involving 22q11 may be seen

Both have eccentrically located eosinophilic cytoplasm

Extrarenal Rhabdoid Tumor	Desmoplastic Small Cell Tumor
No desmoplastic stroma	Prominent desmoplastic stroma
Desmin negative	Desmin positive
INI1 loss 85%	INI1 expressed 100%
Median age 8-9 years	Mean age 25 years
Various deletions, translocations involving 22q11	t(11;22)(p13;q12)