Case report: myxoid atypical fibroxanthoma: a challenging diagnosis of a rare variant

Background: Atypical fibroxanthoma is a cutaneous benign tumor of uncertain lineage, occurring more frequently in elder men, in sun-exposed or irradiated skin. It appears as a slowly progressing nodule, and it is treated by total excision. Several histological types have been described including the myxoid atypical fibroxanthoma. Case presentation: A 73-year-old male presented at the plastic surgery department for excision of a single hard, centrally ulcerated, nodule on the right side of the scalp, 4.1 cm in maximum diameter growing slowly during the last years. The microscopical examination revealed a circumscribed, cellular tumor developing in the dermis. The cellular population consisted of spindle cells and histiocytes, without a specific growth pattern. Moderate cytologic and nuclear atypia were observed, combined with a relatively high mitotic rate. Also, many positive areas of myxoid degeneration detected with periodic acid Schiff and Alcian Blue stains were revealed. Immunohistochemistry showed positivity of the tumor cells for CD10, FXIIIa and focally for CD68, CD117, smooth muscle actin (SMA), and CD99. Tumor cells were negative for all the other assessed markers, including S-100 and Desmin. Ki-67 was 20%. Based on these morphological findings, the diagnosis of myxoid atypical fibroxanthoma was made. Conclusion: Atypical fibroxanthoma is a benign lesion, the diagnosis of which may be proved difficult and challenging. Moreover, when we deal with a rare histologic variant, such as the atypical fibroxanthoma with myxoid change, only the strict application of histological criteria combined with the immunohistochemical findings can lead us to the correct diagnosis, excluding malignant, easily recurring, and metastasizing neoplasms.