Skin nonmelanocytic tumor
Fibrous, fibrohistiocytic and myofibroblastic neoplasms
Atypical fibroxanthoma
Author: Hillary Rose Elwood, M.D.
Topic Completed: 1 November 2016
Minor changes: 28 September 2020
Copyright: 2002-2020, PathologyOutlines.com, Inc.
PubMed Search: Atypical fibroxanthoma [title] skin
Table of Contents
Definition / general | Clinical features | Case reports | Treatment | Clinical images | Gross description | Microscopic (histologic) description | Microscopic (histologic) images | Immunohistochemistry | Electron microscopy description | Molecular / cytogenetics description | Videos | Sample pathology report | Differential diagnosisCite this page: Elwood HR. Atypical fibroxanthoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skintumornonmelanocyticAFX.html. Accessed October 20th, 2020.
Definition / general
- Dermal variant of undifferentiated pleomorphic sarcoma
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
- 21 year old woman with nasal nodule (Can J Plast Surg 2007;15:169)
- 81 year old woman with lower leg lesion (Dermatol Online J 2008;14:6)
Treatment
- Wide local excision
- Mohs micrographic surgery also effective (Dermatol Surg 2009;35:765)
- Excellent prognosis after complete excision
- Rarely recurs or metastasizes
Clinical images
Images hosted on other servers:
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
AFIP images
Marked cellularity and pleomorphism
Characteristic bizarre cells
Spindle variant
Contributed by Dr. Angel Fernandez-Florez
CD68
CD10
AE1 / AE3
Images hosted on other servers:
Ulcerated tumor
Spindle and epithelioid cells with atypia
Nodular spindle cell tumor
Immunohistochemistry
- Immunohistochemistry is imperative in excluding histologic mimics (see differential diagnosis)
- The staining pattern of AFX is nonspecific and the diagnosis is largely one of exclusion based on negative staining for other markers
- A typical immunohistochemical panel for AFX includes:
- High molecular cytokeratin, such as CK5 / CK6 and p63: Negative in AFX (helps to exclude a spindled squamous cell carcinoma)
- S100: negative in AFX (helps to exclude a spindled melanoma)
- Desmin: usually negative in AFX (helps to exclude a pleomorphic leiomyosarcoma)
- CD10: positive in AFX but nonspecific as this marker is widely expressed in other entities
- Many other stains have been reported positive in AFX but none of these are helpful in differentiating from the histologic mimics
- For completeness, positive stains reported include: CD68, alpha-1-antitrypsin, alpha-1-antichymotrypsin, Factor XIIIa (focal), CD117 (Am J Dermatopathol 2008;30:34), CD99 (73%, Am J Clin Pathol 2002;117:126), CD10 (Australas J Dermatol 2005;46:235), CD163, D2-40 (50%, J Cutan Pathol 2011;38:631), calponin (30%, Virchows Arch 2002;440:404), desmin (30%), smooth muscle actin (30%), CD31 (5%)
Electron microscopy description
- Myofibroblasts, fibroblasts and primitive mesenchymal cells
Molecular / cytogenetics description
- Diploid
Videos
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
