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Case Reports

Abstract

A 42-year-old female presented with a reddish-brown textured plaque on her right upper back. The shave biopsy measured 1.5 cm x 0.8 cm and was submitted under the clinical differential of a neoplasm of uncertain behavior versus dermatofibroma versus an accessory nipple in an "odd place". Histological evaluation revealed epidermal hyperplasia with foci of sebaceous lobules, along with a relatively circumscribed dermal proliferation of fibroblasts and histiocytes interposing within dense collagen. No significant cytologic atypia was noted. Subsequently, a diagnosis of dermatofibroma with sebaceous induction was made. Clinically, the lesion mimicked an ectopic nipple with the presence of superficial sebaceous lobules likely resembling Montgomery tubercles. While there have been previous cases describing dermatofibromas with sebaceous induction, this case presents a rare instance of dermatofibromas mimicking an accessory nipple outside the embryonic milk line. Additionally, previous reports have described the opposite phenomenon in which supernumerary nipples and breast tissue have often exhibited features similar to dermatofibromas, both on gross appearance and on dermoscopy. This novel case highlights the potential for clinicopathologic mimicry that deviates from the hallmark features of dermatofibromas, contributing to the growing number of variants observed in these benign tumors.