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Dermatofibrosarcoma protuberans (DFSP) is a fibrous tumor of intermediate malignant potential that usually affects the trunk of young to middle-aged adults. On histological examination, it is characterized by a monomorphous population of spindle cells arranged in a storiform or cartwheel pattern. Bednár tumor (BT), formerly known as storiform pigmented neurofibroma, is currently considered the pigmented variant of DFSP due to the histological and cytogenetic similarities between these two lesions. There are very few reports on BT affecting pediatric patients. We describe a case of BT affecting the dorsal aspect of the left forearm of a 6-year-old-male patient and emphasize the diagnostic clues to distinguish this unusual cutaneous neoplasm from other pigmented lesions, including pigmented (melanotic) neurofibroma (PMN), psammomatous melanotic schwannoma (PMS), neurocristic cutaneous hamartoma (NCH), and desmoplastic malignant melanoma (DMM). We would like to stress that surgical pathologists and dermatopathologists need to be aware of the prototypical histological appearance of BT as there is the risk of misdiagnosing it either as pigmented tumors associated with neurocutaneous syndromes, such as PMN and PMS, or as a highly malignant melanocytic neoplasm (DMM).

A case of dermatofibrosarcoma protuberans (DFSP) with epithelial membrane antigen (EMA)-positive cells is described. The tumor was excised from the left groin of a 28-year-old woman. It showed characteristic histologic features of DFSP with typical diffuse immunohistochemical positivity for CD34. Moreover, scattered neoplastic cells expressed EMA, suggesting perineural cell differentiation. Ultrastructural study found perineurial cell features, such as thin long bipolar cytoplasmic processes, pinocytotic vesicles, fragments of external lamina and/or external lamina-like material, attachment plaques, and desmosome-like junctions. This observation, together with previous immunohistochemical findings of EMA-positive cells in a subset of DFSPs, strongly suggests perineurial cell differentiation in these tumors. DFSP should be included in the differential diagnosis of EMA-positive spindle cell lesions of superficial soft tissue and skin.

Dermatofibrosarcoma protuberans (DFSP) with fibrosarcomatous areas (DFSP-FS) is differentiated from ordinary DFSP by its unfavourable prognosis. We carried out sequential analysis of numerical chromosomal abnormalities in two cases of DFSP during their progression to metastatic disease with FS areas (DFSP-M-FS). They were compared with nine cases of ordinary DFSP and three cases of DFSP-FS, but without metastases. Numerical chromosomal changes were examined by fluorescence in situ hybridization (FISH) using alpha-satellite centromeric probes for chromosomes 1, 8, 11 and 17. Numerical imbalances of chromosome 1 were not clarified. A gain of chromosome 8 was demonstrated in the two cases of DFSP-M-FS. A gain of chromosome 11 was observed in one of the two cases of DFSP-M-FS and in one case of DFSP-FS. A gain of chromosome 17 was demonstrated in both metastatic tumours and in recurrent tumours in two cases of DFSP-M-FS, in addition to two cases of DFSP-FS and four cases of ordinary DFSP with recurrent tumours or large tumours. This study raised the hypothesis that a gain of chromosome 17 developed in recurrent or large-sized DFSP, which occurs in high-risk groups with the possibility of a progression to FS.

The histological and immunohistochemical features of four tumors displaying the characteristic pattern of Giant Cell Fibroblastoma (GCF) are presented. Three of them were found in association with classical and/or myxoid dermatofibrosarcoma protuberans, while the fourth tumor was a retroperitoneal malignant hemangiopericytoma where foci with features of GCF were found. Typical sinusoidal spaces and the bizarre mononuclear and multinucleated cells in close association to blood vessels presenting a wide spectrum of lesions of their walls are also described. These last changes led us to believe that GCF-like lesions might not always characterize an entity but could often represent a host reaction of the connective tissue to locally aggressive or malignant tumors.