<unk>  lesions are incidental findings without reliable clinical correlations. Routine mammograms showing suspicious radiologic findings warrant a core needle biopsy in the abnormal area seen radiologically, and may or may not show<unk>  neoplasia histologically. Morphology<unk> , H&E, 20x Classically, LN, including<unk> , is characterized by enlargement and distension of acini making up the TDLU by proliferation of monomorphic, dyshesive, small, round, or polygonal cells with loss of polarity and inconspicuous cytoplasm. Essentially, groups of round, almost identical looking cells that fill and expand the lobule spaces, occasionally extending into the adjacent terminal ducts – termed Pagetoid extension. Like the cells of atypical<unk>  hyperplasia and invasive<unk><unk> , the abnormal cells of<unk>  consist of small cells with oval or round nuclei and small nucleoli detached from each other. Mucin-containing signet-ring cells are commonly seen.<unk>  generally leaves the underlying architecture intact and recognisable as lobules. Estrogen and progesterone receptors are present and HER2/neu overexpression is absent in most cases of<unk> . Cell borders are indistinct and neither mitotic activity or necrosis are seen. In addition, in<unk>  and invasive lesions exhibit loss of cellular adhesion, considered a characteristic histologic feature, due to the fact that e-cadherin expression is lost (transmembrane protein involved in epithelial cell adhesion). ALH and<unk>  are cytologically indistinguishable, so a quantitative threshold is used to classify lesions into either category. A diagnosis of<unk>  requires more than half of the acini in an involved<unk>  unit to be filled with LN cells and the central lumen of the acini should not be visible. Proliferation of LN cells that do not meet these histological characteristics are either Atypical<unk>  Hyperplasia or simply<unk>  distension. Small degrees of cytologic variation can be observed and subsequent subtypes have been described. However, these subtypes have not been shown to be of clinical usefulness and does not have bearing on whether or not<unk>  will progress to full invasive<unk> . Immunohistochemistry<unk>  may mimic low grade Ductal<unk>  In<unk>  histologically. In these scenarios, pathologists may employ immunohistochemical testing to differentiate between entities. This involves using marked antibodies synthetically developed to bind to target proteins expressed on or inside cells. Specifically, in<unk> , antibodies targeting the e-cadherin protein (or lack thereof) and p120 catenin proteins are used to differentiate<unk>  from DCIS. Due to the fact that<unk>  shows lack of e-cadherin expression on cell membranes and subsequent p120 catenin buildup in the cytoplasm, lesions that show positive membrane immunoreactivity for e-cadherin are diagnosed as DCIS.
Lobular carcinoma in situ
Ductal carcinoma in situ
Sister Mary Joseph nodule
Invasive lobular carcinoma
Invasive carcinoma of no special type
Lymphoepithelioma-like carcinoma
Focal nodular hyperplasia
Atypical ductal hyperplasia