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Soft Tissue Tumors Part 3 - Muscle, Vascular, Nerve, Other

Pleomorphic rhabdomyosarcoma

Author: Nat Pernick, M.D, PathologyOutlines.com, Inc.

Revised: 24 July 2009, last major update July 2009

Copyright: (c) 2002-2009, PathologyOutlines.com, Inc.

Definition

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● High grade sarcoma of adults with bizarre polygonal, round or spindle cells, with skeletal muscle differentiation and no alveolar or embryonal component

Epidemiology

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● Rare; usually age 50+ but can occur in children (Ann Diagn Pathol 2001;5:199)

● Common rhabdomyosarcoma subtype in adults

● 70% male

Clinical

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● Rapidly growing painful mass, most commonly of lower extremity, abdomen / retroperitoneum, chest / abdominal wall or spermatic cord / testes

● Similar behavior to other pleomorphic sarcomas

Case Reports

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● 34 year old man with scrotal tumor (Nippon Hinyokika Gakkai Zasshi 2009;100:545)

● 71 year old woman with retroperitoneal tumor with osteoclast-like giant cells (Archives 2005;129:703)

Treatment and prognosis

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● Poor prognosis

● 70% die of disease after mean follow-up of 20 months (Mod Path 2001;14:595)

Requirements for diagnosis

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● Cross striations or skeletal muscle marker immunoreactivity (i.e. must prove skeletal muscle differentiation)

● No alveolar or embryonal component

● Common errors involve entrapped skeletal muscle, non-specific myoglobin immunoreactivity or skeletal muscle differentiation of other tumors

Gross description

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● Mean 7 cm, up to 30 cm

● May be confined to fascial compartment and assume shape of muscle from which it arises

● White and firm cut surface with variable hemorrhage and necrosis

Micro description

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● Well circumscribed

● Large, multinucleated, bizarre, eosinophilic tumor cells

● Should see cross striations or have immunohistochemical evidence of skeletal muscle differentiation

● No alveolar or embryonal component (by definition)

● Classic type: predominantly atypical rhabdomyoblasts in sheets

● Round cell type: clusters of rhabdomyoblasts in background of slightly atypical, medium sized, round blue rhabdomyoblasts

● Spindle cell type: scattered rhabdomyoblasts with predominantly atypical spindled rhabdomyoblasts in storiform pattern

Micro images

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Classic type with sheets of                             Round cell type with                          Spindle cell type

atypical rhabdomyoblasts                               pleomorphic rhabdomyoblasts

Fascicular pattern                                              Storiform pattern                               Patternless pattern

Hemangiopericytoma-like pattern                 Spindle cells                                        Pleomorphic and

polygonal cells

Epithelioid cells with                                          Clear cytoplasm due to                     Bizarre tumor cells

abundant eosinophilic cytoplasm                  washing out of glycogen

Fig B: rhabdomyoblasts have                          H&E and various stains   

muscle filaments and cross striations

Tumor of psoas muscle with tumor cells exhibiting abundant eosinophilic cytoplasm with hyaline like inclusions (fig 3) and osteoclast-like giant cells (fig 4)

Positive stains

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● Myoglobin (>90%), desmin (>90%), muscle specific actin (70%)

● MyoD1 (50%), skeletal muscle myogenin (50%), smooth muscle actin (50%)

Electron microscopy

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● Skeletal muscle differentiation with rudimentary sarcomeres containing Z bands or Z band material with thick and thin filaments

Electron microscopy images

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Thick and thin filaments from primitive Z bands

Molecular / cytogenetics

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● Complex karyotype (Cancer Genet Cytogenet 2009;192:1)

Differential diagnosis

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● Embryonal or alveolar rhabdomyosarcoma with pleomorphism

● Pleomorphic liposarcoma

● MFH-pleomorphic - diagnosis of exclusion, no evidence of skeletal muscle differentiation

● Sarcoma with heterologous rhabdomyosarcomatous differentiation - differentiated features are characteristic of primary tumor

End of Soft Tissue Tumors Part 3 - Muscle, Vascular, Nerve, Other > Pleomorphic rhabdomyosarcoma

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