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Soft Tissue Tumors Part 3 - Muscle, Vascular, Nerve, Other
Rhabdomyosarcoma - general
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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● Primitive malignant soft tissue sarcoma with skeletal muscle phenotype by H&E, immunohistochemistry or EM
● Subtypes: alveolar, anaplastic, embryonal, pleomorphic, sclerosing (Mod Path 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)
● 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
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
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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 Jun 17 [Epub ahead of print])
● Pathologists should compare post-treatment to pre-treatment specimens (AJCP 2005;123:75)
Positive stains
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● Recommended panel contains myogenin, sarcomeric actin (90%) and desmin (95%)
● Desmin - reliable for solid variant of alveolar rhabdomyosarcoma, positive in 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 Path 2000;13:988)
● MyoD1
● Vimentin (not specific)
Negative stains
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● FLI-1
Electron microscopy
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● Rhabdomyoblasts contain sarcomeres (thick and thin filaments) and Z bands
Additional references
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● Archives 2006;130:1454, Archives 2003;127:1290 (reporting protocol)
End of Soft Tissue Tumors Part 3 - Muscle, Vascular, Nerve, Other > Rhabdomyosarcoma - general
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