Infiltrating syringomatous adenoma of the nipple is a rare, benign, infiltrating neoplasm of eccrine origin located in the dermis of the areola and nipple region first described by Rosen in 1983 [1
]. Lack of metastasis is the rule, but local recurrences can occur when the neoplasm is incompletely excised. Clinically the lesion forms a sub-areolar nodule with variable pain, erythema, nipple distortion, and nipple discharge [2
]. The lesion is almost exclusively present in females, with only one reported case occurring in a male [1
Grossly, infiltrating syringomatous adenoma of the nipple is typically a sub-areolar dermal nodule. Histologically, the epidermis may show variable acanthosis and pseudo-epitheliomatous hyperplasia. Within the dermis there is an infiltrate of curved, ductular structures lined by flattened-to-cuboidal cells, often with proteinaceous debris and skin-type keratin seen in their lumens. The lesion may involve adjacent lactiferous ducts and keratinous cysts are frequently seen. The comma-shaped ducts infiltrate amongst smooth muscle bundles and nerves, simulating a malignant mammary neoplasm. Unlike sclerosing syringomatous carcinoma (sclerosing sweat duct carcinoma), which is typified by deep, vertical stromal infiltration and prominent peri-neural spread, the infiltrating ductules of infiltrating syringomatous adenoma of the nipple show a broad-based and horizontal pattern of infiltration [3
]. Histological features of tubular carcinoma of the breast including angulation of tubules and adjacent ductal carcinoma in-situ, are lacking in infiltrating syringomatous adenoma of the nipple. The hyperplasia of florid papillomatosis of the nipple and the nuclear pleomorphism, necrosis, and increased mitotic index seen in invasive ductal carcinoma are absent in infiltrating syringomatous adenoma of the nipple. The epithelial cell proliferation and the prominent stromal and basement membrane elements seen in adenoid cystic carcinoma are lacking in infiltrating syringomatous adenoma of the nipple [4
]. Histologically, infiltrating syringomatous adenoma of the nipple is not much different from the syringoma that typically occurs on the lower eyelids and pubic area of women.
Complete excision is curative, with local recurrences occurring in 30% of incompletely excised lesions. A single case of possible micrometastasis to a sentinel lymph node from such a tumor has been reported [5
]. Infiltrating syringomatous adenoma of the nipple clinically simulates an underlying mammary malignancy and therefore typically comes to the attention of the surgeon and surgical pathologist rather than the dermatologist and dermatopathologist. Some patients had undergone mastectomy because of misinterpretation of the lesion as a tubular carcinoma [6
] or an adenosquamous carcinoma [2
]. Infiltrating syringomatous adenoma of the nipple is a rare, benign, locally infiltrating neoplasm of eccrine origin that should enter into the differential diagnosis of any sub-areolar nodule.