cutaneous fibrous histiocytoma

PO

Digital cases

 UI:923 - benign fibrous histiocytoma (dermatofibroma)
 PathConsult
 JRC:10461 : Dermatofibroma (fibrous histiocytoma) (Vs. gram cct)

Images

 pallisading dermatofibroma

• https://twitter.com/DrLaurenStuart/status/638769772184895488

 lipidized fibrous histiocytoma

• https://twitter.com/histiocytosisX/status/738028559013400576

 dermatofibroma with basaloid induction

• https://twitter.com/JJSpeiserMD/status/740209809820143616

Definition: Benign proliferation of dermal fibroblasts and histiocytes that generally presents as an asymptomatic, variably pigmented nodule, often on the extremities. Type of fibrohistiocytic tumors.

Clinical synopsis

 Firm
 Nodular
 Nonencapsulated
 Often pigmented
 Chiefly on extremities
 Single or multiple
 Flat, polypoid or depressed shape
 Most @<@1 cm diameter
 Some reach huge proportions

Pathogenesis

 Longstanding controversy as to whether:

• neoplastic
  • favored by occurrence of aggressive and even metastasizing forms
  • evidence of clonality3–5

• reactive

Gross Pathology

 Usually solid
 Rather well circumscribed
 Not encapsulated
 Colored white to yellow to dark brown depending on relative amounts of:

• fibrous tissue
• fat
• hemosiderin

Histopathology

 Characteristically centered in upper dermis
 Can involve deep dermis
 Occasionally extends into subcutis
 Cellular fibroblastic proliferation
 Varying amounts of collagen deposition
 Variable number of macrophages

• fat (foamy appearance)
• hemosiderin (The tumor is mainly composed of hemosiderin-laden macrophages.)
• some multinucleated cells
• may acquire features of Touton’s giant cells
• more rarely osteoclast-like features with or without bone formation.

 Fine vascular network:

• can be prominent
• responsible for: past diagnosis as sclerosing hemangioma
• occasional misdiagnosis as Kaposi’s sarcoma, especially in HIV infection

 May be:

• focal storiform features:
• rarely as well developed as in dermatofibrosarcoma protuberans
• smooth muscle proliferation within adjacent dermis

 Lesions blend imperceptibly into adjacent dermis

 Overlying epidermis:

• normal, atrophic, or acanthotic
• sometimes proliferation of hair germ-like structures in basal layer of epithelium
• This lesion can be associated with basaloid proliferation of the overlying skin. (This change does not represent a basal cell carcinoma)
• rarely basal cell carcinoma develops
• exceptionally squamous cell carcinoma in situ

Morphologic variations (sometimes two or more coexist)

 prominent palisading similar to that in peripheral nerve tumors
 keloid-like changes
 myxoid changes
 granular cells
 markedly lipidized cells
 clear cells
 diffuse eosinophilic infiltrate
 lichenoid, erosive, and ulcerated features
 lipidized fibrous histiocytoma

• https://twitter.com/histiocytosisX/status/738028559013400576

Variants

 marked focal cellular atypia (manifested by ‘monster cells’)
 extreme cellularity (sometimes with necrosis)
 large cystic changes filled with blood: referred to as hemorrhagic aneurysmal or angiomatoid (distinguish from angiomatoid malignant fibrous histiocytoma seen in deeper sites in younger patients)
 epithelioid cell histiocytoma

• mainly large ‘angulated’ epithelioid cells
• notorious for simulating vascular and melanocytic neoplasms

 cellular fibrous histiocytoma
 aneurysmal fibrous histiocytoma
 atypical fibrous histiocytoma (pseudosarcomatous fibrous histiocytoma)
 epithelioid dermatofibroma (epithelioid fibrous histiocytoma)
 ossifying dermatofibroma with osteoclast-like giant cells
 metastasizing "benign" cutaneous fibrous histiocytoma (23426120)

Special Stains and Immunohistochemistry

 Proliferating spindle cells:

• positive for: vimentin
• usually negative for: lysozyme, other histiocytic markers (these results raise questions about alleged histiocytic nature)

 reactive for:

• FXIIIa: a proenzyme in ‘dermal dendrocytes’

 negative for CD34 (in contrast with dermatofibrosarcoma protuberans)
 positive for tenascin

 Often markers associated with smooth muscle/myofibroblastic differentiation:

• e.g. actin, desmin, myosin
• not generally known; has led to misdiagnoses such as leiomyoma and leiomyosarcoma

Immunochemistry

 strong tenascin positivity at the dermal-epidermal junction overlying the lesion (100%)
 tenascin within the DF lesion (80%)
 CD34+ (25%) DF
 Factor XIIIa+ (95%) dermatofibrosarcoma

Differential Diagnosis

 melanocytic nevus
 Kaposi sarcoma
 malignant melanoma
 DFSP (11172295)

Marker	dermatofibroma	DFSP
CD34	25%	80%
FXIIIa	95%	15%
Tenascin in the tumor	80%	80%
Tenascin at the dermal-epidermal junction	100%	0%

 When heavily pigmented may be confused with:

• melanocytic nevi
• malignant melanoma
• Kaposi sarcoma
• other vascular tumors

Prognosis

 Generally indolent
 Local recurrence rare, even if margins inadequate
 Rarely:

• locally aggressive

 Exceptionally rarely:

• distant metastases
  • more common if: in face, deep extension into subcutaneous tissue or cellular fascicles of mitotically active spindle cells

See also

 fibrohistiocytic tumors

• angiomatoid fibrous histiocytoma (specific tumoral entity)

References

 Metastasizing "benign" cutaneous fibrous histiocytoma: a clinicopathologic analysis of 16 cases. Doyle LA, Fletcher CD. Am J Surg Pathol. 2013 Apr;37(4):484-95. doi : 10.1097/PAS.0b013e31827070d4 PMID: 23426120

 Kaddu S, McMenamin ME, Fletcher CD. Atypical fibrous histiocytoma of the skin: clinicopathologic analysis of 59 cases with evidence of infrequent metastasis. Am J Surg Pathol. 2002;26:35–46.

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 Calonje E, Fletcher CDM. Aneurysmal benign fibrous histiocytoma. Clinico pathological analysis of 40 cases of a tumour frequently misdiagnosed as a vascular neoplasm. Histopathology. 1995;26:323–332.

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