Abstract

Nevus sebaceus (NS) is a congenital malformation involving the pilosebaceous units and hair follicles of the skin. The usual sites of involvement include the scalp and face, and hormonal changes occurring at puberty can cause growth and change in appearance. Rarely secondary adnexal/follicular neoplasms, both benign and malignant, can arise in association with NS. Our patient is a 16-year-old female with a 1 cm linear pink-orange plaque on her face with no other significant medical history. Her lesion was stable until recently, when she developed a 4 mm papule within it. Biopsy of the lesion showed hyperkeratosis, an acanthotic epidermis with a papillomatous pattern and some abnormally formed hair follicles and sebaceous glands consistent with NS. Arising from NS is an adnexal neoplasm with prominent ductular differentiation (confirmed by a CEA stain) and an infiltrative growth pattern consistent with microcystic adnexal carcinoma (MAC). Secondary neoplasms arising from NS are usually benign with trichoblastoma and syringocystadenoma papilliferum being the most common benign tumors described. Basal cell carcinoma is the most common malignant secondary neoplasm, with other entities like sebaceous carcinoma, squamous cell carcinoma, and microcystic adnexal carcinoma being very rare and usually arising in older individuals. MAC arising in NS is rare itself, and the young age of presentation makes this case worthwhile to add to the current literature.