Non-invasive Lobular Neoplasia: Review and Updates.

Non-invasive lobular neoplasia (LN) encompasses atypical lobular hyperplasia (ALH), classic lobular carcinoma in situ (CLCIS), florid lobular carcinoma in situ (FLCIS), and pleomorphic lobular carcinoma in situ (PLCIS). Lobular neoplasia is a neoplastic epithelial proliferation of the terminal duct lobular unit. A defining feature is discohesion due to the loss of E-cadherin, a protein that facilitates cell-to-cell adhesion. Lobular neoplasia is both a risk factor and a non-obligate precursor of invasive breast carcinoma. Classic LN, characterized by small, non-cohesive monomorphic cells, includes ALH and classic LCIS. While classic LN is usually not seen on imaging and, therefore, is diagnosed incidentally, FLCIS and PLCIS are typically the imaging targets, most often manifesting as calcifications. Unlike classic LN, which is typically hormone receptor-positive and HER2-negative, FLCIS and PLCIS may present with less favorable phenotypes. While ALH and CLCIS diagnosed on concordant core biopsy are generally managed with surveillance with or without chemoprevention, complete surgical excision is recommended for FLCIS and PLCIS due to high upgrade rates to invasive carcinoma. Accurate classification of non-invasive breast neoplastic lesions is essential for guiding treatment. This review provides an overview of the clinical features, pathology, and management of lobular neoplasia, emphasizing the importance of accurate diagnosis and individualized patient care.