Surgical Pathology Criteria

Rhabdomyosarcoma

Differential Diagnosis

Embryonal rhabdomyosarcoma

  Nblast ALL Ewing Sarc (PNET) Rhabdo MNTI DSCT Wilms Tumor
Synapto pos neg neg neg pos neg neg
NB84 pos neg neg neg neg neg neg
CD45RB (LCA) neg pos neg neg neg neg neg
CD99 neg pos pos neg rare neg neg
Myogenin neg neg neg pos rare neg neg
MyoD1 neg neg neg pos neg neg neg
Keratin neg neg rare rare pos pos neg
Desmin neg neg neg pos rare pos neg
WT1(C) neg neg neg neg neg pos pos
S100 neg neg rare neg rare neg neg
HMB45 neg neg neg neg pos neg neg
Nblast = Neuroblastoma; ALL = Precursor T Lymphoblastic Leukemia; Rhabdo = Rhabdomyosarcoma; MNTI = Melanotic Neuroectodermal Tumor of Infancy; DSCT = Desmoplastic Small (Round) Cell Tumor; Synapto = Synaptophysin

The small cell pattern of DSCT may be confused with rhabdomyosarcoma. Both are desmin positive.

Embryonal Rhabdomyosarcoma Desmoplastic Small Cell Tumor
No desmoplastic stroma Prominent desmoplastic stroma
Keratin variable, faint and focal Keratin 90% positive, prominent
EMA negative EMA 90% positive
WT1 rare, focal WT1 positive
Muscle actin positive 95% Muscle actin rare
Median age 7 years Mean age 25 years
No consistent genetic abnormality t(11;22)(p13;q12)

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

Alveolar rhabdomyosarcoma Alveolar Soft Part Sarcoma
Variably shaped alveolar spaces Regular alveolar spaces
Fibrous septa around nests Thin walled vascular septa
Cells generally 10-30 microns diameter Cells larger
Pleomorphic nuclei Only mild pleomorphism
Dense nuclei Vesicular nuclei
Small nucleoli Prominent nucleoli
No crystals Crystals in up to 80% of cases
Uniformly desmin, actin positive Occasionally desmin, actin positive
Frequently MyoD1 positive MyoD1 rare or negative
Translocations t(2;13) or t(1;13) der(17)t(X;17)(p11.2;q25)

Sclerosing Rhabdomyosarcoma Desmoplastic Small Cell Tumor
Keratin 5-50% positive, focal, weak Keratin 90% positive, prominent
EMA negative EMA 90% positive
WT1(C) negative WT1(C) positive
Any age group Mean age 25 years
No consistent genetic abnormality t(11;22)(p13;q12)
Both are desmin positive with a prominent sclerotic/desmoplastic stroma

Pleomorphic Rhabdomyosarcoma High Grade Pleomorphic Sarcoma (MFH)
Myogenin and/or MyoD1 positive Myogenin and MyoD1 negative
Desmin positive Desmin reactivity infrequent
Both may have pleomorphic cells with abundant eosinophilic cytoplasm and cross striations are not typically seen in either

Pleomorphic Rhabdomyosarcoma Embryonal Rhabdomyosarcoma with Numerous Round Differentiated Myoblasts
Rare in children, peak incidence in 5th decade Most occur in children, typically children < 10 years of age
Lacks uniform background of immature cells Has uniform background of immature cells
Nuclei of large cells are very pleomorphic Nuclei of large cells typically uniform

Pleomorphic Rhabdomyosarcoma Alveolar Rhabdomyosarcoma with Multinucleated Giant Cells
Rare in children, peak incidence in 5th decade Most occur in children
Lacks uniform background of immature cells Has uniform background of immature cells
Nuclei of large cells are very pleomorphic Nuclei of giant cells typically uniform and located in a peripheral ring
Lacks mutations involving PAX8-FOXO1 Mutations involving PAX8-FOXO1 in 80%

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