Atypical Fibroxanthoma Presenting as a Rapidly Enlarging Tender Papule: Case Report

Atypical fibroxanthoma (AFX) is a rare dermal mesenchymal neoplasm that is most commonly identified on sun-exposed areas of the head and neck of older adults. Presentation on the dorsal hand is uncommon.

This report presents a rare case of AFX, its clinical presentation, histopathology, and treatment, and discusses the use of immunohistochemistry as a method in diagnosing AFX.

We evaluated a 67-year-old woman with a history of basal cell and squamous cell carcinomas who presented with a rapidly enlarging, tender papule on the dorsal aspect of her left hand. Prior topical 5-fluorouracil therapy was ineffective. Histopathologic examination demonstrated findings favoring AFX, and treatment was initiated. A literature review was performed to contextualize this case among previously reported instances of AFX.

Clinical examination revealed a 1.2-cm, dome-shaped, erythematous papule. Histopathology demonstrated a dermal-based pleomorphic spindle cell neoplasm with brisk mitotic activity. Immunohistochemistry showed positivity for CD68 and CD10, with negative staining for SOX10, PRAME, pankeratin, p40, SMA, desmin, and CD34. The morphologic and immunohistochemical findings favored AFX. The tumor was completely excised via Mohs micrographic surgery (MMS) in a single stage with negative margins. No adjuvant therapy was required.

AFX remains a diagnosis of exclusion requiring comprehensive immunohistochemistry to distinguish it from morphologic mimics with aggressive biologic behavior. This case highlights that MMS is the preferred treatment for AFX, offering the lowest recurrence rates with maximal tissue conservation.