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Skin / Soft Tissue Tumors

Fibrohistiocytic Tumors

Atypical fibrous histiocytoma


Reviewer: Vijay Shankar, M.D. (see Reviewers page)
Revised: 16 December 2014, last major update August 2012
Copyright: (c) 2003-2014, PathologyOutlines.com, Inc.

General
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● Cellular, circumscribed dermal lesion of spindled fibroblasts, myofibroblasts, histiocyte-like cells and often giant cells
● Marked nuclear pleomorphism and mitotic figures (often atypical)
● No tumor cell necrosis
● No vascular invasion

Terminology
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● Rare variant of cutaneous fibrous histiocytoma
● Also called pseudosarcomatous fibrous histiocytoma or dermatofibroma with monster cells
● Part of WHO classification for skin tumors, not soft tissue tumors
● First described in 1983 (J Cutan Pathol 1983;10:327)

Epidemiology
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● Median age 38 years (range 5-90 years), no gender preference

Sites
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● Solitary lesions usually arise on extremities or trunk (Am J Dermatopathol 1986;8:467)
● Also head and neck, vulva, rarely scrotum

Case reports
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● 25 year old woman with recurrent leg lesion (Eur J Dermatol 1998;8:122)
● 62 year old woman with leg lesion (Tokai J Exp Clin Med 2004;29:49)
● 64 year old woman with 3 cm back lesion (Am J Dermatopathol 2002;24:36)
● 79 year old woman with leg lesion (Am J Dermatopathol 1997;19:312)
● 90 year old man with scrotal lesion (Ann Diagn Pathol 2003;7:370)

Treatment and prognosis
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● May be misdiagnosed as sarcoma (Histopathology 1990;17:167)
● Complete excision with negative margins
● Occasional local recurrence (14%) or distant metastasis (Am J Surg Pathol 2002;26:35)

Clinical images
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Exophytic nodular lesion of abdominal wall

Gross description
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● Median 1.5 cm (0.4 to 8 cm), nodular or polypoid

Micro description
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● Involvement of dermis and superficial subcutaneous tissue by pleomorphic, plump, spindle or polyhedral cells with large hyperchromatic, irregular or bizarre nuclei
● Background of classic fibrous histiocytoma including epidermal hyperplasia, Grenz zone, spindle cells with storiform pattern and entrapped thick collagen bundles, especially at periphery
● Variable multinucleated giant cells, often with bizarre nuclei (“monster cells”, Am J Dermatopathol 1987;9:380) and foamy or hemosiderin-rich cytoplasm
● Mild to marked pleomorphism
● 0-15 mitotic figures/10 HPF, frequently atypical
● Necrosis occasionally present

Micro images
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Enlarged cells with hyperchromatic nuclei, but no / rare mitotic figures (source: AFIP Fascicle, 3rd series)

Positive stains
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● Vimentin, Factor XIIIa, CD34 (occasionally)

Negative stains
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● CD68, actin, desmin, CD10, S100, keratin (MNF116), EMA; < 1% positive for MIB1 (Am J Dermatopathol 2004;26:367)

Differential diagnosis
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Atypical fibroxanthoma: sun damaged areas of head and neck in elderly, presents as dome shaped or ulcerated nodule, tumor cells abut epidermis without a grenz zone; also marked actinic elastosis, no classic features of fibrous histiocytoma
Dermatofibrosarcoma protuberans: strongly positive for CD34, lacks pleomorphism
Nodular melanoma: S100+
Pleomorphic fibroma: hypocellular, no epidermal hyperplasia, no classic features of fibrous histiocytoma
MFH-pleomorphic or other pleomorphic sarcomas: infiltrative, marked atypia, brisk mitotic activity, necrosis; no classic features of fibrous histiocytoma
Spindle cell squamous cell carcinoma: cytoketatin positive

End of Skin / Soft Tissue Tumors > Fibrohistiocytic Tumors > Atypical fibrous histiocytoma


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