Comprehensive Immunohistochemical Analysis of Atypical Fibroxanthoma: Focus on PRAME in Differential Diagnosis.

BACKGROUND

Atypical fibroxanthoma (AFX) is an uncommon cutaneous neoplasm predominantly affecting elderly individuals in sun-exposed areas. Despite its alarming histopathological features, AFX typically exhibits an indolent clinical course. Diagnosis remains challenging due to overlapping features with other aggressive cutaneous malignancies, especially malignant melanoma.

METHODS

We retrospectively analyzed 15 cases of AFX diagnosed between 2009 and 2024. Comprehensive immunohistochemical profiling was performed, including CD10, CD68, S100, Melan-A, HMB45, CD31, CD34, ERG, cytokeratins, P40, P63, SMA, Desmin, and newly, PRAME (clone EPR20330). Clinical and follow-up data were collected from medical records.

RESULTS

The cohort had a mean age of 72.9 years, with a male predominance (66.7%). The scalp was the most frequent tumor site (40.0%). All cases demonstrated diffuse block-type CD10 positivity and were uniformly negative for PRAME. Occasional weak staining for melanocytic markers was observed in a minority of cases. After a mean follow-up of 84.0 months, all patients were alive.

CONCLUSION

A comprehensive immunohistochemical panel is essential for the accurate diagnosis of AFX. The absence of PRAME expression, together with block-type CD10 positivity, supports the distinction of AFX from malignant melanoma and other histological mimics, facilitating appropriate clinical management.