Atypical Fibroxanthoma

Abstract

Atypical fibroxanthoma (AFX) is a nodular dermal ulcerative lesion with a favorable prognosis. AFX most commonly occurs on sun-exposed skin in elderly individuals. AFX is characterized by its association with ultraviolet radiation, not only from a clinical aspect, but also from a molecular aspect. Making a diagnosis of AFX is challenging, and it is important to differentiate it from squamous cell carcinoma and malignant melanoma. Histological features and combined immunohistochemical markers are necessary for a definitive diagnosis (i.e., an absence of immunostaining for cytokeratins, S100 and HMB45 in AFX is helpful for excluding both squamous cell carcinoma and malignant melanoma). AFX, as well as MFH (malignant fibrous histiocytoma), is a fibrohistiocytic lesion with myofibroblastic differentiation. AFX is considered to be a different lesion from MFH. AFX and MFH might share the same pathway which determines their morphology. However, they may have different pathways in development which determine their biological behavior.

An Uncommon Case of Atypical Fibroxanthoma of the Bulbar Conjunctiva

“…Of the five other reported cases, four were found at the limbus, as in our patient [1][2][3][4]. The typical histologic presentation of AFX is spindle, plump, epithelioid and bizarre cells, in various proportions, arranged in haphazard, vaguely fascicular or storiform patterns [4]. Often, there is fibroblastic, myofibroblastic, and epithelioid cells with pleomorphism noted [5].…”

“…Often, there is fibroblastic, myofibroblastic, and epithelioid cells with pleomorphism noted [5]. Some cells of the lesion may contain vacuolated and lipid-containing cytoplasm similar to a xanthoma [4]. Most of the reported cases of conjunctival AFX have been either spindle-cell predominant or pleomorphic with epithelioid and multinucleated giant cells [1].…”

“…S-100 is positive in malignant melanoma. However, dendritic/Langerhans cells within AFX may express S-100 ( Figure 2F) [4]. Cytokeratin is positive in squamous cell carcinoma but not AFX.…”

“…A histiocytic/macrophage marker, CD68, is positive in more than half of all AFX cases ( Figure 2C). However, D68 is also detectable in 86% of malignant melanoma cases [4]. Therefore, this marker can rule out squamous cell carcinoma but not melanoma.…”

“…It is reported that about one third of melanomas and half of squamous cell carcinomas are also positive for CD10. However, melanomas and squamous cell carcinomas stained weakly, with majority accumulating in the stroma [4]. When using immunohistochemical staining to diagnose AFX it is important to known these possible variations.…”