Cytologic features of nipple adenoma: a report of four cases of adenoma of the nipple.

We report four cases of adenoma of the nipple, a rare benign epithelial benign tumor occurring under the nipple and areola. Clinically, erosion findings of the nipple require discrimination from Paget's disease. In addition, a mass found in the nipple warrants discrimination from ductal carcinoma. Two cases underwent aspiration biopsy cytology and the other underwent tumor imprint cytology, respectively, revealing a large number of epithelial cell populations in the necrotic background material. These large cell clusters had a papillary or sheet structure and exhibited decreased cell cohesiveness at the cluster part. In addition, small clusters and solitary epithelial cells were also present. Furthermore, a two-cell pattern comprising both duct epithelial and myoepithelial cells was observed in the cell clusters. Two other cases underwent nipple brush cytology, revealing a few small papillary clusters with isolated epithelial cells in the hemorrhagic background. The clusters appeared as benign duct proliferative lesions such as papilloma, papillomatosis, and adenosis. An accurate diagnosis warrants the recognition of regular nuclei with bland chromatin and myoepithelial cells and the identification of the lesion location.