Epitheliosis (or usual duct hyperplasia) is a proliferation of epithelial and myoepithelial cells located within enlarged acini and small ducts, which is characterized by irregular and peripheral fenestration. Infiltrating epitheliosis (IE) is a specific lesion, characterized by classical epitheliosis flowing out into the adjacent stroma. The stroma is desmoplastic and shows keloid appearance with irregular elastosis. IE can mimic malignancy both on radiological and histological grounds. The aim of the present study is to describe the fine needle aspiration cytological features of 6 consecutive cases of IE, with histological correlation. IE cases presenting as screen detected lesions and preoperatively diagnosed on fine needle aspiration cytology (FNAC) were reviewed. All patients had radiologically breast lesions suspicious for malignancy that underwent FNAC followed by surgical resection. The FNAC smears presented some features that could lead to a misdiagnosis of malignancy, such as bloody background, high cellularity, and stromal fragments containing epithelial cells. Nevertheless, malignancy was excluded, due to the absence of atypia and the presence of myoepithelial cells in the cell clusters. IE presents a special FNAC pattern that can be misinterpreted as malignancy. Therefore, knowledge is necessary to avoid patient overtreatment.
Keywords: breast; cytology; fine needle aspiration cytology; infiltrating epitheliosis.