Soft tissue tumors - Rhabdomyosarcoma

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Soft tissue tumors

Skeletal muscle

Rhabdomyosarcoma - general

Reviewer: Vijay Shankar, M.D. (see Reviewers page)
Revised: 21 February 2013, last major update November 2012
Copyright: (c) 2003-2013, PathologyOutlines.com, Inc.

Definition
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● Primitive malignant soft tissue sarcoma with skeletal muscle phenotype by H&E, immunohistochemistry or EM
● Subtypes: alveolar, anaplastic, embryonal, pleomorphic, sclerosing (Mod Pathol 2001;14:506), although mixtures are common
● Note: some alveolar and embryonal tumors have similar gene expression (Am J Pathol 2009;174:550)

Epidemiology
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● Most common soft tissue sarcoma of childhood/adolescence (5-8% of solid pediatric tumors, 50% of pediatric soft tissue sarcomas)
● 50% at 0-9 years
● Children 2-6 years usually have head, neck or GU tumors
● Teenagers usually have paratesticular, trunk or abdominal tumors
● Relatively rare in adults, who often have pleomorphic and NOS subtypes
● Slight male predominance (M/F: 1.3:1)
● Head and neck tumor are more often embryonal types
● Extremity tumors more often have alveolar histologic type
● 80% of genitourinary RMS are embryonal type
● Usually >5 cm at diagnosis

Rhabdomyoblast
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● Cell of origin for rhabdomyosarcomas
● Eccentric eosinophilic granular cytoplasm rich in thick and thin filaments
● If round and elongate, are called strap cells or tadpole cells

Clinical description
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● Needle biopsies may be sufficient for accurate diagnosis (Pediatr Blood Cancer 2009;53:356)
● Usually aneuploid

Treatment and prognosis
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● International Classification of Rhabdomyosarcoma (Cancer 1995;76:1073)
- Superior prognosis: botryoid, spindle cell
- Intermediate prognosis: embryonal
- Poor prognosis: alveolar, undifferentiated sarcoma
● Adults have poorer 5 year survival (27%) than children (61%, J Clin Oncol 2009;27:3391)
● Poorer overall 5 year survival in hand/foot (33% versus 56% overall) due to marked tendency to spread and inability to completely excise (Pediatr Hematol Oncol 2009;26:321)
● Poorer survival in childhood embryonal (intermediate-risk) tumors if anaplasia is present (Cancer 2008;113:3242)
● Five year survival has increased from periods 1976-1980 to 1996-2000 for rhabdomyosarcoma overall (53% to 62%), embryonal (61% to 73%) and alveolar subtypes (40% to 48%, Cancer 2009;115:4218)
● Pathologists should compare post-treatment to pre-treatment specimens (Am J Clin Pathol 2005;123:75)

Micro images
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Various images

Positive stains
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● Recommended panel contains myogenin, sarcomeric actin (90%) and desmin (95%)
● Desmin: reliable for solid variant of alveolar rhabdomyosarcoma, tumors with round or strap cell rhabdomyoblasts, also smooth muscle tumors
● Myoglobin: specific, but only found in better differentiated tumors, may be non-specific due to diffusion from adjacent injured skeletal muscle cells
● Myogenin: sensitive and specific, particularly useful for alveolar subtype (Mod Pathol 2000;13:988)
● MyoD1
● Vimentin (not specific)

Negative stains
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● FLI-1

Electron microscopy description
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● Rhabdomyoblasts contain sarcomeres (thick and thin filaments) and Z bands

Additional references
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● Arch Pathol Lab Med 2006;130:1454, Arch Pathol Lab Med 2003;127:1290, ISRN Oncol 2012;2012:674523

End of Soft tissue tumors > Skeletal muscle > Rhabdomyosarcoma - general

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