Flat epithelial atypia is an entity that comprises any columnar cell lesion with low-grade cytologic atypia.
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Terminology
Flat epithelial atypia was introduced in the 3rd edition of WHO Classification of Breast Tumors in 2003, to substitute terms such as clinging carcinoma monomorphous type, atypical cystic lobules, atypical lobules type A, atypical columnar change and ductal intraepithelial neoplasia 1A 1.
Pathology
Flat epithelial atypia is characterized by enlarged terminal ductal lobular units with dilated acini and consisting of one or more layers of cuboidal or columnar epithelial cells with cytologic atypia and monomorphic round to oval nuclei 1,2.
Radiographic features
Amorphous and fine pleomorphic microcalcifications.
Treatment and prognosis
Excision is generally recommended as it may represent either a precursor to or the earliest morphologic manifestation of low-grade ductal-carcinoma-in-situ, as well as a precursor to invasive carcinoma (low grade), more frequently tubular carcinoma 2.
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