Atypical dermatofibroma with predominant epithelioid/deciduoid-like cell component. Histogenetic considerations in the wide spectrum of fibrohistiocytic dermal tumours.

Atypical and epithelioid cell variants of dermatofibroma may represent a potential diagnostic pitfall. Only rarely atypical dermatofibroma may show focal epithelioid cell features. We herein report a rare case of dermatofibroma composed of a predominant (> 90%) epithelioid/deciduoid-like cell component, in which rare multinucleated bizarre cells and atypical mitoses were additional findings. Tumour was classified as "atypical dermatofibroma with predominant epithelioid/deciduoid-like cell component". The coexistence of at least two different variants, i.e. epithelioid and atypical variants, in the same dermatofibroma suggests that dermal fibrohistiocytic tumours belong to a continuous morphological spectrum. Accordingly, the morphological variants of dermatofibroma should be regarded as variations on a common basic theme. Differential diagnosis with other epitheliod cell dermal tumour- and tumour-like lesions is discussed.