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Soft Tissue Tumors Part 3 - Muscle, Vascular, Nerve, Other
Embryonal 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.
Subtypes: embryonal-NOS, anaplastic, botryoid, spindle cell
Definition
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● Primitive soft tissue sarcoma with small blue cells resembling embryonic skeletal muscle
● Most common rhabdomyosarcoma subtype (65%)
Epidemiology and sites
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● Usually children ages 3-10 years, in nasal and oral cavities, orbit, middle ear, prostate, paratesticular region
● Rare in skin, thoracic cavity
● Associated with prenatal Xrays in one study (Cancer Epidemiol Biomarkers Prev 2009;18:1271)
● May be associated with hypercalcemia thorough increased parathormone production
● Metastasizes to soft tissue, serosa, lung, lymph nodes and bone marrow
● Extremity involvemen is uncommon and associated with more relapses and lower survival
Treatment and prognosis
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● Excision, chemotherapy, radiation therapy
● Favorable prognostic factors are younger patients, spindle and botyroid variants in young patients, GU location (survival of 90%+ after excision and chemotherapy), localized tumor (survival of 80%)
Gross description
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● Poorly circumscribed mass, white, soft or firm, infiltrative
Gross images
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Images: intramuscular white tumor with central necrosis (subtype not specified)
Micro description
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● Sheets of small, spindled or moderate to poorly differentiated round cells with scant or deeply eosinophilic cytoplasm and eccentric, small oval nuclei
● Highly cellular areas around blood vessels alternate with parvicellular mucoid regions (resembles normal embryonal myogenesis)
● Cross striations in 50%
● Rarely has anaplastic features (see anaplastic variant), clear cell change, rhabdoid features, neuronal, melanocytic or schwannian differentiation (ectomesenchymoma)
● More differentiation typically occurs post-chemotherapy or radiotherapy
Positive stains
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● Vimentin in all cells (even most primitive)
● Some cells should stain for desmin, MyoD1 or myogenin
● Actin and desmin staining in more differentiated cells
● PAS highlights glycogen in most tumors
● c-kit (15%), myogenin (rare to 25% of tumor cells, Mod Path 2000;13:988)
Cytology description
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● Cellular with features of a small round cell tumor
● Rarely intranuclear cytoplasmic inclusions (Diagn Cytopathol 2009 Jun 15 [Epub ahead of print])
Electron microscopy
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● Developing striated muscle, thick and thin filaments
Molecular / cytogenetics
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● loss of 11p15; +2q, +8, +12, +13, +20
● No N-myc amplification
● Congenital cases are associated with t(2;8)(q35;q13) involving PAX3 gene (Cancer Genet Cytogenet 2009;191:43)
● No diagnostic translocation found to date
Differential diagnosis
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● Desmoplastic small round cell tumor - presents with tumor nodules on serosal surfaces, may be desmin+ but strongly keratin+ and EMA+, muscle specific actin-
● Ewing’s / PNET - often rosettes, nuclei are uniform and pale, not dense and hyperchromatic; CD99+, desmin-, muscle specific actin-, t(11;22)+
● Large cell lymphoma - CD45+, B/T cell markers present, desmin-, muscle specific actin-
● Neuroblastoma - elevated urinary catecholamines, rosettes, granular chromatin, S100+ (often), chromogranin+, GFAP+
● Rhabdomyoma
● Undifferentiated sarcoma - negative for muscle markers
End of Soft Tissue Tumors Part 3 - Muscle, Vascular, Nerve, Other > Embryonal rhabdomyosarcoma
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