A challenging case of giant atypical fibroxanthoma on non-chronically sun-damaged skin: a case report with TP53 somatic mutation (c.375+1 G>A).

Atypical fibroxanthoma (AFX) is a rare tumor of uncertain histogenetic origin, generally seen in elderly patients' chronically sun-damaged skin, most frequently in the head and neck region. Due to the absence of specific histopathologic features, AFX is a diagnosis of exclusion. Herein, we report clinical, histopathological, and molecular features of a young patient with a recurrent and giant AFX lesion on non-chronically sun-damaged skin. Histologically, the tumor was well-circumscribed, encapsulated, and dermal-based, composed of highly atypical and pleomorphic bizarre spindled cells with hyperchromatic and irregular nuclei and scarce multinucleated giant cells. There was no subcutaneous invasion, necrosis, or perineural/perivascular invasion. Tumoral cells were diffusely and strongly positive for CD10 but negative for melanocytic, cytokeratin, and muscle immunohistochemical markers. Almost five years after the excision, no recurrence and/or distant metastasis was observed. A pathogenic variant of a TP53 somatic mutation (c.375+1 G>A) was identified in the tumor.