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We have reported a case of cellular fibrous histiocytoma occurring as a polypoid, dermal nodule in the arm of a 10-year old boy. The tumour was predominantly composed of spindleshaped cells with a mild degree of nuclear pleomorphism and showed unusual morphological features like central necrosis and epidermal ulceration. Apart from vimentin and CD10, surprisingly, neoplastic cells were diffusely stained with an epithelial membrane antigen. Although expression of the epithelial membrane antigen is absent in conventional fibrous histiocytomas, immunoreactivity for this marker has been reported in about 60% of dermal epithelioid cell fibrous histiocytomas. Case report A 10-year old boy presented to our observation with a non-painful, solitary, polypoid, cutaneous lesion; the lesion was focally ulcerated, measuring 1 cm in its greatest diameter, and located in the right arm. This is the first case of cellular fibrous histiocytoma, which exhibited diffused expression of the epithelial membrane antigen. The presence of tumour necrosis and epidermal ulceration, along with an aberrant expression of the epithelial membrane antigen, raised serious diagnostic problems, leading to a speculation regarding the presence of epithelioid sarcoma. Conclusion Immunohistochemical analyses, showing diffused nuclear INI1 (hSNF5/SMARCB1) expression and the absence of pancytokeratins, were extremely helpful in ruling out epithelioid sarcoma. Awareness of the possibility that dermal cellular fibrous histiocytoma may concurrently exhibit necrosis, epidermal ulceration and diffused expression of epithelial membrane antigen, is crucial to avoid a misdiagnosis of malignancy. Introduction Fibrous histiocytoma is a common fibro-histiocytic tumour which commonly occurs in the dermis and superficial subcutis (dermatofibroma). The diagnosis of dermatofibroma/fibrous histiocytoma is usually straightforward if the typical morphological features are present1–3. However, some diagnostic difficulties may arise when one is dealing with some unusual morphological variants, including cellular1,3,4, lipidised2,3, haemosiderotic3,4, aneurysmal1–4, keloidal3,4, granular cell2–4, palisading3,4, atrophic1–4, clear cell1–4, myxoid4, lichenoid3,4, balloon cell3,4, signet-ring cell3,4, with osteoclastlike giant cells4,5, with smooth muscle proliferation4, with prominent myofibroblastic proliferation4, with intracytoplasmic eosinophilic globules4, plexiform3,4, epithelioid1,3,4,6–8, atypical1–4,9,10 and lastly, combined variants11,12. Among these variants, cellular fibrous histiocytoma (CFH) may represent a diagnostic challenge because there is the risk of it being confused with other benign or malignant dermal tumours1,3, 4. CFH, first described by Calonje et al.13 as a distinct variant of fibrous histiocytoma, accounts to approximately 5% of cutaneous benign fibrous histiocytomas (dermatofibromas) . CFH generally presents in young to middle-aged adults as a slowly growing, solitary nodule, ranging in size from 0.5 cm to 2.5 cm, with a slight male predominance13. Although CFH has the tendency to develop in the same anatomic sites to those for conventional fibrous histiocytoma, it may occur at unusual sites such as the face, ears, hands and feet13. Over the last two decades, there has been increasing evidence that CFH undergoes local recurrence more than the usual fibrous histiocytomas (rates of 25%)1–3, especially after incomplete surgical excision1,2,13. Unlike conventional fibrous histiocytomas, characteristic morphological features of CFH are (i) higher cellularity, (ii) higher mitotic activity (up to 10 mitoses per high-power field), (iii) a more fascicular growth pattern, (iv) a deeper (subcutaneous) tumour extension, (v) a higher tendency to exhibit an epithelioid cell compo* Corresponding author Email: g.musumeci@unict.it 1 Department G.F. Ingrassia, Azienda Ospedaliero-Universitaria ‘Policlinico-Vittorio Emanuele’ Anatomic Pathology, University of Catania, Catania, Italy 2 Department of Bio-Medical Sciences, Human Anatomy and Histology Division, University of Catania, Catania, Italy 3 Department of Bio-medical Sciences, Section of Physiology, University of Catania, Catania, Italy 4 Anatomic Pathology Unit, Azienda USL Lanciano-Vasto, Chieti, Italy De rm at ol og y

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Aberrant epithelial membrane antigen expression in dermal cellular fibrous histiocytoma with central necrosis and epidermal ulceration: a potential mimicker of epithelioid sarcoma