Atypical fibroxanthoma (AFX) is a rare primary skin neoplasm of presumable mesenchymal derivation but of uncertain histogenetic origin. AFX was used as a diagnostic term likely several years prior to 1964.2 Since then and until recently, AFX was an issue of ongoing controversy for decades. The major controversies concerned 1) the histogenetic origin of the neoplasm and, hence, the most appropriate terminology to be used for it, 2) the most valuable diagnostic immunophenotypic markers (if any), to be used to verify diagnosis and, 3) the pertinent features allowing reliable and reproducible separation of AFX from its many mimics. The latter point was particularly further complicated by the many faces and histological patterns encountered in AFX, either as a focal pattern, or as the predominant or the sole pattern.1, 2, 3, 4, 5

The current terminology for this neoplasm, already coined prior to 1964, reflects the histogenetic assumption that the tumors cells display fibroblastic and histiocytic cell features with variable xanthomatous cell component. However, the descriptive cytological terminology applies as well to undifferentiated pleomorphic sarcoma of deep soft tissue, for which the term malignant fibrous xanthoma was used by Stout6 prior to the “malignant fibrous histiocytoma” terminology which was coined subsequently for that highly aggressive soft tissue entity.7 Notably, this morphological/ cytological pattern is shared by a variety of undifferentiated malignancies irrespective of their histogenetic origin, underlying the low specificity of the fibroxanthomatous pattern which reflects an “undifferentiated mesenchymal status” rather than representing a specific line of differentiation.8,9