Becker nevus syndrome presented with ipsilateral breast hypoplasia

Becker nevus syndrome (BNS) is a rare epidermal nevus syndrome characterized with Becker nevus and ipsilateral breast gland hypoplasia or other skin, skeletal and/or muscle tissue disorders. A 24-year-old woman presented with brown, irregular bordered patch with a diameter of approximately 10 cm which consisted of several small macules on the left breast skin. The ultrasonography and magnetic resonance imaging revealed left breast hypoplasia. Histopathological examination demonstrated minimal acanthosis, papillomatosis, increase in basal layer melanin and hypertrophy of the erector pili muscle. Immunohistochemical staining was positive for androgen in the epidermis, dermal stromal cells and skin appendages. Depending on the clinical and histopathological findings, the patient was diagnosed as BNS. Diagnosis of BNS needs careful examination of pigmented macules and patches since non-hairy BN may be easily overlooked. Patients with BN should be evaluated for associated abnormalities of BNS, in which the severity and extend of ectodermal involvement may differ from patient to other.