Skin nonmelanocytic tumor
Fibrous, fibrohistiocytic and myofibroblastic neoplasms
Atypical fibroxanthoma

Topic Completed: 1 November 2016

Minor changes: 14 July 2020

Copyright: 2002-2019,, Inc.

PubMed Search: Atypical fibroxanthoma [title] skin

Hillary Rose Elwood, M.D.
Page views in 2019: 14,267
Page views in 2020 to date: 10,549
Cite this page: Elwood HR. Atypical fibroxanthoma. website. Accessed August 14th, 2020.
Definition / general
Clinical features
  • Typically found on sun damaged skin of elderly patients, particularly head and neck
  • Rapidly growing, small, dome shaped or polypoid nodule, sometimes ulcerated
  • Size < 2 cm in diameter
  • Clinical appearance not distinctive and clinical differential diagnosis includes carcinoma
Case reports
  • Wide local excision
  • Mohs micrographic surgery also effective (Dermatol Surg 2009;35:765)
  • Excellent prognosis after complete excision
  • Rarely recurs or metastasizes
Clinical images

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Irregular polypoid tumors

21 year old woman with nasal nodule

Solitary dome shaped nodule

Gross description
  • Papule to nodule, sometimes ulcerated; < 2 cm
Microscopic (histologic) description
  • Well circumscribed dermal nodule usually within skin showing solar damage (e.g. solar elastosis)
  • Tumor often abuts the epidermis but rarely may have a grenz zone of uninvolved dermis
  • Spindled to round or epithelioid tumor cells in haphazard or fascicular pattern
  • Bizarre multinucleated pleomorphic cells present
  • Frequent mitotic figures; many atypical mitotic figures
  • Resembles undifferentiated pleomorphic sarcoma but centered in dermis
  • The tumor should not extensively involve the subcutaneous tissue (if it does, the lesion may represent a pleomorphic dermal sarcoma)
  • No invasion of deeper structures (i.e. muscle or fascia) should be present (if it is, the lesion may represent a pleomorphic dermal sarcoma)
  • Histologic variants: angiomatoid, chondroid, clear cell (J Cutan Pathol 2006;33:343), granular cell (Am J Dermatopathol 2007;29:84), keloidal (J Cutan Pathol 2009;36:535), myxoid (J Cutan Pathol 2009;36:1177), osteoclastic, osteoid, pigmented (Actas Dermosifiliogr 2009;100:321)
Microscopic (histologic) images

Images hosted on PathOut servers:

Marked cellularity and pleomorphism

Characteristic bizarre cells

Spindle variant has less pleomorphism

Tumor is limited to dermis but otherwise
resembles MFH pleomorphic with marked
cellularity, prominent pleomorphism,
mitotic figures and clumped chromatin

CD68 (left), CD10 (middle) and AE1 / AE3 (right)
Above 6 images contributed by Dr. Angel Fernandez-Florez

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Ulcerated tumor

Spindle and epithelioid cells with atypia

Nodular spindle cell tumor

Fig 1: eyebrow primary
Fig 2 - 4: facial metastasis
(fig 4 is CD68)

Electron microscopy description
  • Myofibroblasts, fibroblasts and primitive mesenchymal cells
Molecular / cytogenetics description
  • Diploid

Atypical fibroxanthoma versus mimics by Dr. Gardner

Sample pathology report
  • Skin, biopsy:
    • Superficially sampled pleomorphic dermal spindle cell neoplasm (see comment)
    • Comment: The histologic differential for these findings includes an atypical fibroxanthoma or a pleomorphic dermal sarcoma. Complete re-excision is recommended along with close clinical followup. If the excision demonstrates this lesion to be superficial, then the findings are those of an atypical fibroxanthoma; however, if the re-excision demonstrates a large or more infiltrative tumor, a pleomorphic dermal sarcoma would be favored.
Differential diagnosis
  • The predominant histologic mimics are those atypical spindle cell neoplasms that abut the epidermis, sometimes referred to as the “SLAM” differential for ease of remembrance (spindled squamous cell carcinoma, leiomyosarcoma, AFX, spindled melanoma)
  • Angiosarcoma: spindle cell variant, prominent vascular spaces or blood, vascular markers+
  • Atypical fibrous histiocytoma
  • Leiomyosarcoma - pleomorphic type: usually more fascicular growth pattern, desmin+
  • Partial biopsy of Pleomorphic dermal sarcoma: superficial aspect of pleomorphic dermal sarcoma (PDS) can appear identical to AFX but on excision a PDS is a much larger and more deeply infiltrative lesion with a worse prognosis
  • Spindled or desmoplastic melanoma: S100+, may have associated atypical intraepidermal melanocytic proliferation (Am J Dermatopathol 2007;29:551)
  • Squamous cell carcinoma - spindle cell type: deep extension, p63+ and high molecular weight cytokeratin positive (J Cutan Pathol 2009;36:543)
  • Of note, the diagnosis of AFX should be avoided or made with caution on superficial biopsies as a superficially sampled pleomorphic dermal sarcoma could appear identical; if I don’t have the base on initial biopsy, I may diagnose as in sample pathology report
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