Abstract

Atypical fibroxanthoma (AFX) is a dermal-based, low-grade malignant mesenchymal neoplasm showing no specific lineage of differentiation, typically arising in the sun-damaged skin, particularly the head and neck region of elderly individuals. AFX with osteoclast-like giant cells form is mentioned in 17 reported cases in the literature. Even though AFX tumors demonstrate worrisome malignant histological features, most of the cases have a very good prognosis with less than 10% local recurrence and exceedingly rare metastasis. It is crucial to differentiate this lesion from other malignant tumors with osteoclast-like giant cells, especially giant cell tumors of the skin, soft tissue, and bone. We report a case of a 77-year-old male patient with a history of multiple basal and squamous cell carcinomas of the skin, who presented with a new, enlarging erythematous nodule on the sun-damaged right central parietal scalp. Sections revealed a dermal malignant spindle cell neoplasm, with abundant osteoclast-like multinucleated giant cells and numerous atypical mitotic figures. Immunohistochemistry demonstrated diffuse positivity for CD68 and SMA, patchy positivity for CD10, and negative for SOX-10, pan-cytokeratin cocktail, CK5/6, S100, CD34, and desmin. The differential diagnoses included giant cell tumors of soft tissue/skin and AFX with osteoclast-like multinucleated giant cells. Based on the histologic and immunophenotypic characteristic features, the lesion was best interpreted as AFX with osteoclast-like multinucleated giant cells. The tumor was completely excised with negative margins. The patient was doing well on 4 months follow-up with no recurrence.

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