[Flat epithelial atypia]

According to the WHO, flat epithelial atypia (FEA) is defined as a neoplastic epithelial proliferation of ductal type in either a single or in multiple terminal duct lobular unit(s) limited to the periphery of the ductules in a clinging growth pattern. The atypical cells may form between one and several layers of epithelial cells that show low grade cytologic atypia. FEA most often presents as mammographic microcalcifications, which are typically round (secretory type and psammomatous calcification in an eosinophilic matrix, so-called ossifying calcifications). Clinical relevance is dependent on whether the lesion appears in isolation or whether it is an excision biopsy or a minimally invasive biopsy. Currently available data suggest that the risk of subsequent breast carcinoma in the ipsilateral breast is very low following the diagnosis of FEA. The differential diagnosis should include atypical ductal hyperplasia, low-grade clinging ductal carcinoma in situ, blunt duct adenosis and apocrine metaplasia.