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Soft tissue tumors

Skeletal muscle

Embryonal rhabdomyosarcoma-general

Reviewer: Vijay Shankar, M.D. (see Reviewers page)
Revised: 12 March 2013, last major update November 2012
Copyright: (c) 2003-2013, 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
● Median age of GU presentation is 13 years (Mod Pathol 2012;25:602)
● Rare in skin, thoracic cavity, esophagus and stomach
● 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 age, spindle and botyroid variants in young patients, GU location (survival of 90%+ after excision and chemotherapy), localized tumor (survival of 80%); also hyperdiploid
● Presence of diffuse anaplasia is negative prognostic factor

Case reports
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● 2 year old boy with parotid mass - gangliorhabdomyosarcoma (Case of the Week #268)
● 16 year old girl with mass of cervix (Afr J Paediatr Surg 2011;8:95)
● 19 year old Caucasian man with jaw swelling (Head Neck Pathol 2010;4:334)
● 24 year old woman with laryngeal tumor (Arch Otolaryngol Head Neck Surg 2011;137:635)
● 30 year old woman with botyroid variant in mesentery (Turk Patoloji Derg 2011;27:84)
● 32 year old woman with soft palate tumor (Indian J Pathol Microbiol 2011;54:136)
● 33 year old man with laryngeal tumor (BMC Cancer 2011;11:166)

Clinical images
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Large exophytic mass emanating from right arytenoid, obstructing laryngeal inlet and obscuring true vocal cords

Gross description
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● Poorly circumscribed mass, white, soft or firm, infiltrative

Gross images
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Various images

Case of the Week #268

Micro description
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● Composed of primitive mesenchymal cells in various stages of myogenesis
● 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

Micro images
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Mandible

     
Mesentery: botyroid variant

   
Soft palate

Myogenin+

Case of the Week #268:

Positive stains
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● Vimentin in all cells (even most primitive)
● Some cells should stain for desmin, MyoD1 or myogenin
● Actin, desmin, myoglobin, myosin, and creatine kinase M staining in more differentiated cells
● PAS highlights glycogen in most tumors
● C-kit (15%), myogenin (rare to 25% of tumor cells, Mod Pathol 2000;13:988)
● Aberrantly these tumors may show immunoreactivity to cytokeratin, S100 protein, neurofilaments, and B cell proteins such as CD20 and immunoglobulins

Cytology description
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● Cellular with features of a small round cell tumor
● Rarely intranuclear cytoplasmic inclusions (Diagn Cytopathol 2009;37:740)

Electron microscopy description
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● Developing striated muscle, thick and thin filaments

Molecular / cytogenetics description
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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)
● Inactivating mutations of TP53 and CDKN2A and activating mutations of RAS family genes
● No diagnostic translocation found to date

Differential diagnosis
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● Desmoplastic small round cell tumor: tumor nodules on serosal surfaces, strongly keratin+ and EMA+, may be desmin+ but 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 > Skeletal muscle > Embryonal rhabdomyosarcoma-general

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