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Case Reports

Abstract

A 66-year-old male presented to dermatology for a longstanding linear verrucous lesion on his left arm that had recently enlarged and become tender. Initial biopsy showed a dermal collection of dilated ducts lined with a double layer of cuboidal cells and filled with amorphous basophilic secretions under a hyperkeratotic, papillomatous, and acanthotic epidermis. A diagnosis of tubulopapillary adenoma was made with the recommendation for excision. However, after discussion with the clinician and review of the patient images, four additional biopsies were obtained from different areas of the lesion due to the clinicopathologic discordance. All specimens showed the same findings, and notably, no enlarged sebaceous lobules were present in any specimen. Tubulopapillary adenoma, or tubular adenoma, describes a spectrum of benign adnexal tumors that is known to be associated with nevus sebaceus. Only one case report exists where a tubulopapillary adenoma arose from a keratinocytic epidermal nevus. Like our case, the tubulopapillary adenomas were multifocal, suggesting that this pattern may be typical of this presentation. Both keratinocytic epidermal nevus and nevus sebaceus can carry RAS mutations, which have also been found in tubulopapillary adenomas. This case adds to the literature suggesting that the clinical differences between keratinocytic epidermal nevus and nevus sebaceus may represent the influence of location in cases of shared genetic background.