Abstract

Distinctive Dermal Clear Cell Mesenchymal Neoplasm (DDCCMN) is a rare tumor characterized by a dermal proliferation of neoplastic cells with clear cytoplasm and vesicular nuclei. Though thought to be mesenchymal in origin, its exact line of differentiation is unknown. We report an instance of a 34 year-old Caucasian male who presented with a 0.8 cm eroded papule on the posterior shoulder. The lesion had progressed in size over a three month period. A biopsy was performed to rule out basal cell carcinoma. Histologic evaluation demonstrated a well-circumscribed collection of polygonal clear cells arranged in sheets with epidermal collarettes. The neoplastic cells resided in the papillary dermis without an intraepidermal component and could be seen enmeshed in the thick collagen fibers of the reticular dermis. The cells were characterized by enlarged round to ovoid pleomorphic nuclei and clear, vacuolated cytoplasm with prominent cytoplasmic membranes. No mitoses were present. Immunohistochemical stains were performed to rule out other clear cell cutaneous neoplasms, balloon cell melanocytic lesions and clear cell metastatic carcinomas. All stains were negative, except for strong positivity for NKI-C3 and a subset of cells which highlighted for CD68; DDCCMN was diagnosed. Presently, DDCCMN is distinguished by morphologic features and strong staining for NKI-C3. CD68 histiocytic marker is also variably positive as first reported by Lazar and Fletcher and later observed by McAlhany and Leboit. Prior case reports have suggested DDCCMN's propensity for appearing on the lower limb. This is the first reported case on the upper extremity.

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