OBJECTIVETo investigate the clinicopathological and immunohistochemical features, diagnosis and differential diagnosis of nipple adenoma of the breast.

METHODSMorphological observation and immunohistochemistry were applied to 18 cases of nipple adenoma with a review of the related literatures.

RESULTSThe neoplasms were localized at nipples or under the areola of breast, adherent to the epidermis, mainly composed of dilated ducts in a tubular appearance associated with fibrotic matrix. The glandular epithelium showed various type of proliferation, forming thick layers or complex structures such as papillae, micropapillae, tufts, fronds, arcades or bridges accompanying with solid or cribriform cell nests. The tumor cells were crowding, lack of an uniform morphology and polarity with intact myoepithelial cells around the ducts. By immunostaining, the glandular epithelium was diffusely positive for 34betaE12, patchily positive for CK5/6, and negative for p53 and c-erbB-2. The myoepithelium, positive for p63, smooth muscle actin and Calponin, was well preserved and outlining the ducts.

CONCLUSIONSNipple adenoma is an infrequent type of benign breast neoplasm, presenting as sclerosing papilloma, papillomatosis or florid sclerosing adenosis. It is easily confused with atypical ductal hyperplasia/low grade ductal carcinoma in situ, invasive ductal carcinoma or low grade adenosquamous carcinoma. A correct diagnosis is based on the peculiar location and morphology of the tumor, and immunohistochemistry is helpful in some cases.