[Practical problems in breast screening. Columnar cell lesions including flat epithelial atypia and lobular neoplasia].

Columnar cell lesions (CCL) and lobular neoplasia (LN) are encountered with increasing frequency in breast screening biopsies. CCLs are frequently associated with microcalcifications, whereas LN is an incidental finding in most cases. Flat epithelia atypia (FEA) the atypical variant of CLL, LN and atypical ductal hyperplasia (ADH) are frequently associated lesions. Molecular genetic studies of CCL, ductal carcinoma in situ (DCIS) and low grade invasive carcinomas revealed similar chromosomal alterations supporting the assumption that CCLs are neoplastic proliferations. The frequent association of FEA together with well differentiated invasive carcinomas provides further evidence of this concept. There is no internationally accepted classification of CCLs at present. CDH1-gene mutations are the cardinal feature of LN and invasive lobular carcinoma. In immunohistochemically CDH1-positive cases, alternative genetic alterations of the CDH1 pathway can lead to functional loss of CDH1. In our opinion morphologically and immunohistochemically hybrid lesions may represent this group of lobular lesions. Recent follow-up data suggest a higher rate of ipsilateral carcinomas in patients with previously diagnosed LN. It is currently an open question whether FEA and LN are members of a common family of intralobular proliferations, which are non-obligatory precursors of a low nuclear grade breast neoplasia family.