Unilateral nevoid acanthosis nigricans with a submammary location

Unilateral nevoid acanthosis nigricans (AN) is an exceedingly rare form of AN, which is a benign disorder of keratinization. The lesions of unilateral nevoid AN are distributed unilaterally while the histopathologic findings are similar to the common form of AN, and this is characterized by hyperkeratosis, papillomatosis and moderate acanthosis. A 19-year-old female presented with asymptomatic brownish pigmented plaques on the medial side of the left submammary area. Based on her clinical and histopathologic findings, a diagnosis of unilateral nevoid AN was made. She was treated with topical tretinoin and her skin lesions were almost cleared 9 months after her first visit to our clinic. Various previous reports have described the localization of this disorder, but there has been no previous case report with the clinical manifestations on the unilateral submammary area. Therefore, we herein report the first case of unilateral nevoid AN with an unusual submammary location.