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 Fibrohistiocytic Tumours

Pathology of Atypical Fibroxanthoma

Dr Sampurna Roy MD              


Dermatopathology Quiz Case 171 

Diagnosis: Atypical Fibroxanthoma (Spindle Cell Variant)

Pathology Quiz Case 21- Case History and images:

Diagnosis: Atypical Fibroxanthoma 




The term 'Atypical Fibroxanthoma, was introduced by Helwig EB (Texas J Med 1963;59: 664-667 ). Similar cases were reported as Paradoxical fibrosarcoma of the skin or pseudosarcoma by Bourne RG (Med J Aus 1963;1:5 04-510).

Microscopic images of Atypical Fibroxanthoma

Clinical presentation:

- The tumour usually presents as solitary, rapidly growing dome shaped ulcerated and crusted nodule, usually less than 2 cm in diameter, on the head or neck  region of the elderly.The lesion usually occurs in sun-damaged or radiation damaged skin.

- A rare clinical variant occurs in younger patients. The tumour is larger and slow growing and are usually located  on the trunk and extremities.

Microscopic features: Image Link1 ; Image Link2 ; Image Link3; Image Link4  

- Exophytic , well circumscribed, non encapsulated tumour.

- Located in the dermis.

- Expansile growth. The tumour is usually bordered by mononuclear inflammatory cells in the deeper aspect.

- The adjacent adnexal structures are usually compressed. Adnexal structures  within the tumour are always intact.

- The overlying epidermis is thin and usually ulcerated with crust formation , but  there may be peripheral epidermal acanthosis with formation of  'epithelial collarette'.

- A thin grenz zone may be present separating the tumour from the epidermis or the tumour may stream out from the basal layer.

In the latter case the dermo-epidermal junction is not always clear.

- The tumour is characterized by marked  pleomorphism and polymorphism .

- There is an admixture of three main cell types: 
 -   Plump spindle shaped cells with vesicular nucleus, arranged in fascicles
    -   Large polyhedral cells. Some of these cells are vacuolated.
    -   Bizarre giant cells (mononucleate  or multinucleate) with hyperchromatic nuclei.

Note: Oil red O stain on frozen sections show  variable amount of lipid in the polyhedral and giant cells.

- Typical and atypical mitotic figures are noted (one per high power field).

- The epidermis overlying the tumour usually do not show evidence of atypia, junctional activity or atypical melanocytes. 

However, epidermis adjacent to the tumour may show evidence of actinic keratosis.

- Dermis adjacent to the main lesion show features of solar elastosis. Telangiectatic blood vessels may be present near the surface.

- In rare cases foci of osteoid and chondroid differentiation and osteoclast like giant cells may be present.

- Spindle cell variant is entirely composed of monomorphic palely eosinophilic spindle shaped cells arranged in fascicles.

There is only mild pleomorphism.  (Differential diagnosis: leiomyosarcoma, spindle cell squamous carcinoma and spindle cell melanoma).

Histologic variants of Atypical Fibroxanthoma :

Spindle cell

Clear cell  




Granular cell



Following features help to exclude Atypical Fibroxanthoma from other lesions:

1. Presence of vascular and / or perineural invasion.

2. Extensive necrosis away from the ulcerated surface.

3. Extensively infiltrative growth pattern.

4. Deep extension into the subcutaneous fat.

Immunohistochemical features:

Vimentin shows diffuse strong cytoplasmic positivity.

Smooth muscle actin shows focal but strong cytoplasmic staining in many cases.

Alpha1- antitrypsin , alpha1- antichymotrypsin , HAM56 (non-specific) are immunopositive.

CD68 (monocyte-macrophage marker) shows some positivity.

CD74 is weakly positive in some cases. (In  MFH CD74 is strongly positive).

In a few cases scattered cells stain positively for factor XIIIa.

Focal positivity for CD99 has been reported.

Differential diagnosis of Atypical Fibroxanthoma:

1. Spindle Cell Squamous Cell Carcinoma: Infiltrative tumour and overlying epidermal dysplasia is present. Cytokeratin is positive.

2. Malignant melanoma: S100 protein and HMB45 positive. Spindle cell melanomas  are usually amelanotic,infiltrative tumour with uniform cytology and are often associated with desmoplasia. Neural invasion may  be present.

3. Leiomyosarcoma:  Infiltrative, poorly circumscribed tumour composed of bundles of spindle cells. Primary cutaneous leiomyosarcoma shows minimal cytological atypia.

Metastatic tumours are well circumscribed and demonstrates prominent cellular atypia. Desmin is positive.

Note:   Immunohistochemical analysis is absolutely essential to confirm the diagnosis.

4. Malignant fibrous histiocytoma (Pleomorphic sarcoma): Deep soft tissue tumour. CD74 is strongly positive.

5. Dermatofibrosarcoma protuberance: Characteristic monomorphic cytology, storiform arrangement.

6. Reticulohistiocytoma: Composed of epithelioid cells with 'ground glass' cytoplasm.

7. Post irradiation: Features similar to atypical fibroxanthoma may be present in post irradiated skin. 

Further reading:

Granular cell atypical fibroxanthoma.

CD10, a useful marker for atypical fibroxanthomas.  

Metastasizing atypical fibroxanthoma (cutaneous malignant histiocytoma): report of five cases.

A rare low-grade malignant scalp tumor Atypical fibroxanthoma.  

The value of immunohistochemistry in atypical cutaneous fibrous histiocytoma.  

HMB-45 (gp103) and MART-1 expression within giant cells in an atypical fibroxanthoma: a case report.

Procollagen 1 expression in atypical fibroxanthoma and other tumors.

Atypical fibrous histiocytoma and atypical fibroxanthoma: presentation of two cases.

Atypical fibroxanthoma with prominent sclerosis.

Atypical fibrous histiocytoma of the skin: clinicopathologic analysis of 59 cases with evidence of infrequent metastasis.

CD99 Immunoreactivity in Atypical Fibroxanthoma. A Common Feature of Diagnostic Value.

CD117 immunoreactivity in atypical fibroxanthoma.

Clear cell atypical fibroxanthoma - report of a case with review of the literature  




Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)






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