Soft tissue tumors - Sclerosing rhabdomyosarcoma

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Soft tissue tumors

Skeletal muscle

Sclerosing rhabdomyosarcoma

Reviewer: Vijay Shankar, M.D. (see Reviewers page)
Revised: 22 February 2013, last major update November 2012
Copyright: (c) 2003-2013, PathologyOutlines.com, Inc.

Definition
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● Rhabdomyosarcoma with extensive hyalinized matrix production (Am J Surg Pathol 2002;26:1175, Am J Clin Pathol 2008;129:410)
● Not a WHO diagnosis
● First described in 2000 (Virchows Arch 2000;436:305)

Clinical features
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● Adults and children (Int J Surg Pathol 2006;14:193)
● Often in head and neck (Laryngoscope 2005;115:48)

Case reports
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● 62 year old man with leg tumor (Virchows Arch 2006;449:572)
● Parotid gland swelling (Ann Diagn Pathol 2009;13:334)

Gross description
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● 4 to 8 cm

Micro description
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● Lobules and infiltrating cords of small round malignant cells embedded in densely hyalinized matrix with chondroid and osteoid-like appearance
● May have pseudovascular growth pattern, rhabdomyoblastic differentiation with strap cells, areas suggestive of spindle cell rhabdomyosarcoma, extensive mitotic activity (>20 mitotic figures/20 high power fields)
● No / focal embryonal or alveolar patterns
● No tumor giant cells
● No definite lacunae or matrix calcification present

Micro images
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Various images

Virtual slides
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Back mass

Positive stains
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● MyoD1 (100%, almost every cell), actin, desmin (focal), myogenin (focal)

Negative stains
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● Cytokeratin, S100

Molecular / cytogenetics description
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● No t(2;13) of alveolar rhabdomyosarcoma
● Specific MDM2/HMGA2 amplification at 12q13-15 in 1 case (Hum Pathol 2009;40:1347)
● Loss of 10q22, loss of chromosome Y and gain of #18 in one case (Virchows Arch 2006;449:572)
● Pattern of numerical changes similar to embryonal rhabdomyosarcoma in one case (Virchows Arch 2005;446:64)
● Hyperdiploidy, tetraploidy, del 1, Trisomy 11, 16, monosomy 22

Electron microscopy description
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● Irregularly distributed disorganized filament in richly collagenized matrix
● No Z-bands

Differential diagnosis
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● Alveolar rhabdomyosarcoma: different morphology; has PAX3 and PAX7-FKHR fusion transcripts (Pediatr Dev Pathol 2004;7:583)
● Angiosarcoma
● Chondrosarcoma: has neoplastic chondroid cells
● Osteosarcoma: has neoplastic osteoid
● Sclerosing epithelioid fibrosarcoma

End of Soft tissue tumors > Skeletal muscle > Sclerosing rhabdomyosarcoma

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