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Breast malignant, males, children

Sarcoma

Low grade myofibroblastic sarcoma


Reviewer: Monika Roychowdhury, M.D. (see Reviewers page)
Revised: 7 November 2012, last major update November 2012
Copyright: (c) 2001-2012, PathologyOutlines.com, Inc.

Definition
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● Rare malignant tumor of myofibroblasts (Am J Surg Pathol 1998;22:1228)

Terminology
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● Also called myofibrosarcoma
● Not part of WHO breast classification

Clinical features
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● Commonly recurs, only rarely metastasizes

Case reports
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● 55 year old woman with death due to metastatic tumor (Am J Surg Pathol 1997;21:489)

Gross description
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● Firm, pale, fibrous cut surface, ill defined margins

Micro description
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● Fascicles of spindle cells surrounded by dense collagen
● Cells have ill defined, pale, eosinophilic cytoplasm, fusiform and pleomorphic nuclei, numerous mitotic figures
● Also some giant cells
● Margins are infiltrative, often grossly (Pathol Res Pract 1999;195:1)

Micro images
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Fig 1A: fascicular growth
Fig 1B: alpha smooth muscle actin+, vimentin+ (insert)
Fig 1C: fibronectin+ matrix
Fig 1D: type IV collagen negative

Positive stains
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● At least one myogenic marker (desmin, alpha smooth muscle actin, muscle specific actin or calponin)

Negative stains
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● S100, EMA, h-caldesmon, ALK

Electron microscopy
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● Features of myofibroblasts: discontinuous basal lamina, abundant rough endoplasmic reticulum, intermediate filaments and myofilaments; indented and clefted nuclei

Electron microscopy images
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Fig 2A: arrows point to thin filaments at the cell surface suggestive of fibronexus junctions
Fig 2B: arrows point to fibronectin fibrils extending into the extracellular matrix

Molecular / cytogenetics description
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● Gains at 1p11-->p36.3 (66%), 12p12.2-->p13.2 (45%), 5p13.2-->p15.3 (31%), +22 (28%), loss at 15q25-->q26.2 (24%) (Am J Clin Pathol 2009;131:701)

Differential diagnosis
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Fibromatosis / myofibromatosis: irregular, nonencapsulated proliferation of spindle cells forming interlacing fascicles with variable collagen deposition and cellularity; no/rare mitotic figures
Fibrosarcoma: highly cellular fibroblastic proliferation in herringbone pattern
Inflammatory myofibroblastic tumor: more heterogeneous, less cellular, less hyperchromasia, less infiltrative, ALK+ (Hum Pathol 2008;39:846)
Leiomyosarcoma: alternating fascicular pattern, usually high grade
Myofibroblastoma: may have some pleomorphism, but low mitotic activity
Nodular fasciitis: not infiltrative, not deep, lacks chromosomal anomalies
Solitary fibrous tumor: patternless architecture of hypo- and hypercellular areas separated by thick, hyalinized collagen with cracking artifact and hemangiopericytoma-like vessels

End of Breast malignant, males, children > Sarcoma > Low grade myofibroblastic sarcoma


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