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Table of Contents
Definition / General | Epidemiology | Clinical Features | Treatment | Micro Images | Positive Stains | Negative Stains | Electron Microscopy Description | Additional ReferencesDefinition / General
- 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)
Rhabdomyoblast
- 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
Epidemiology
- 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
Clinical Features
- Needle biopsies may be sufficient for accurate diagnosis (Pediatr Blood Cancer 2009;53:356)
- Usually aneuploid
Treatment
- 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
Images hosted on other servers:
Various images
Positive Stains
- 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
Electron Microscopy Description
- Rhabdomyoblasts contain sarcomeres (thick and thin filaments) and Z bands
Additional References
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