Definition
A superficial pleomorphic tumour usually occurring on sun-damaged skin, indistinguishable histologically from a pleomorphic malignant fibrous histiocytoma. Atypical fibroxanthoma is no longer considered a fibrohistiocytic lesion, but is probably a UV-induced proliferation of dermal fibroblasts.
Synonyms
Pseudosarcoma of the skin, paradoxical fibrosarcoma, pseudosarcomatous dermatofibroma, pseudosarcomatous reticulohistiocytoma
Most cases occur in sun-damaged skin on the head or neck of the elderly, less often on the hands. About 25% of cases occur on the limbs of younger adults. Prior irradiation may be causative.
There is a single nodule, which may bleed.
There is an expansile dermal nodule which may extend into the subcutis. The epidermis may show atrophy or ulceration. The tumour consists of bizarre cells which may be spindled or round, rarely forming a storiform pattern. There are numerous mitotic figures, some atypical. Necrosis is rare. Rare clear cell and granular variants have been reported. The adjacent skin shows solar elastosis. Significant subcutaneous invasion should exclude a diagnosis of atypical fibroxanthoma.
Variant:
spindle cell non-pleomorphic atypical fibroxanthoma
Immunohistochemistry is mainly of value in excluding other entities which form the differential diagnosis.
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positive |
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focally positive |
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negative |
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negative |
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negative |
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The features are those of a mesenchymal tumour.
Spindle cell (sarcomatoid) carcinoma
Leiomyosarcoma, primary or metastatic
Atypical benign fibrous histiocytoma: a more likely diagnosis on skin that is not sun-damaged or in young adults.
Behaviour is almost always benign. Recurrences may occur but, if strict diagnostic criteria are applied, metastases almost never occur.
This page last revised 3.5.2005.
©SMUHT/PW Bishop