Abstract

Tubular adenoma is a rare benign dermal neoplasm of sweat gland origin that represents a spectrum of adnexal tumors with varying degrees of apocrine and eccrine differentiation, ranging from tubular apocrine adenoma to papillary eccrine adenoma. They typically present as firm dome-shaped nodules. To our knowledge, only 3 tubular adenomas presenting as cutaneous horns have been reported to date. Here, we present a 48-year-old white male who presented with a right upper arm lesion of several years duration that had been unresponsive to over-the-counter topical salicylic acid. Skin examination revealed a 7x7 mm raised papule with central keratotic plug, clinically suggestive of a cutaneous horn with underlying verruca, basal cell carcinoma or squamous cell carcinoma. A deep scoop shave biopsy was performed. Histopathologic examination demonstrated verruciform papillomatous epidermal proliferation with parakeratosis overlying a relatively well-demarcated neoplasm located in the superficial and deep dermis. The dermal neoplasm was composed of oval to elongated islands of bilayered to multilayered squamoid and cuboidal epithelial cells including a myoepithelial outer layer with formation of variably sized lumina some of which were slit-like. Some lumina contained granular gray-to-eosinophilic material, a portion of which appeared keratinized. Occasional calcifications were noted within the islands and the background dermis. No significant atypia or mitotic activity was identified. A diagnosis of papillary eccrine adenoma (tubular adenoma) with overlying verruca-like proliferation was rendered. It is our aim to share this uncommon benign sweat gland neoplasm and highlight its unusual clinical presentation as a cutaneous horn.

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