Flat epithelial atypia (DIN 1a, atypical columnar change): an underdiagnosed entity very frequently coexisting with lobular neoplasia

Aims: Flat epithelial atypia of the breast [FEA; synonyms: ductal intraepithelial neoplasia (DIN) 1a, atypical columnar change] is increasingly recognized by pathologists and shows distinct genetic alterations. The aim of this study was to determine its biological significance as an incidental finding in breast biopsy specimens. Methods and results: On the assumption that both FEA and lobular neoplasia (LN) derive from progenitor cells in the terminal ductal-lobular unit, we investigated the association between FEA and LN semiquantitatively in 111 excisional breast biopsy specimens which contained LN, but did not contain ductal carcinoma in situ (DCIS) or invasive carcinoma. Ninety-six cases (86.5%) revealed coexistence of LN and FEA (P < 0001). The distribution of LN was focal in 41 cases (37%), multifocal in 50 (45%) and extensive in 20 (18%) cases. FEA was identified as focal, multifocal and extensive in 29 (26%), 42 (38%) and 25 (23%) cases, respectively. Distribution patterns of LN and FEA showed no statistically significant correlation. Conclusions: Due to the striking association between LN and FEA in our material, one may speculate that these two lesions are biologically related and that FEA is an early but non-obligate precursor lesion similar to LN. Based on this assumption, regular clinical and mammographic follow-up of patients with FEA would be prudent.