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Stains
Factor XIIIa
Reviewer: Nat Pernick, M.D. (see Reviewers
page)
Revised: 9 August 2012, last major update August 2012
Copyright: (c) 2002-2012, PathologyOutlines.com, Inc.
Definition
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● Fibrohistiocytic marker; note that peritumoral cells may also exhibit Factor XIIIa staining
● Also active form of factor XIII, an enzyme of coagulation system that crosslinks fibrin (Wikipedia)
Uses by pathologists
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● Marker of fibrohistiocytic proliferations
● Marker of dermal dencrocytes
● Differentiate dermatofibrosarcoma protuberans (CD34+, D2-40-, Factor XIIIa-) from dermatofibroma (CD34-, Factor XIIIa+, D2-40+)
Micro images
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Atypical fibroxanthoma

Dermatofibroma

Epithelioid fibrous histiocytoma
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Fibrohistiocytic proliferation with dermal nevus (fig c)
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Fibrohistiocytic proliferation with melanoma (fig c)
Positive staining - normal
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● Dermal dendrocytes
Positive staining - disease
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● Soft tissue: benign fibrous histiocytoma and variants, malignant fibrous histiocytoma
● Also calcifying fibrous tumor (Mod Pathol 2001;14:784), verruciform xanthoma
● Also atypical fibroxanthoma (focal), hemangiopericytoma (scattered), myofibroblastoma in lymph nodes (variable), pleomorphic hyalinizing angiectatic tumor (focal), storiform collagenoma (scattered)
● Cervix: aggressive angiomyxoma
● CNS: Erdheim-Chester disease
Negative staining
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● Dermatofibrosarcoma protuberans (usually), Langerhans cell histiocytosis
● Solitary fibrous tumor (Int J Gynecol Pathol 2010;29:189)
End of Stains > Factor XIIIa
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