Lobular carcinoma in situ

Lobular carcinoma in situ (LCIS) is an incidental microscopic finding with characteristic cellular morphology and multifocal tissue patterns. The condition is a laboratory diagnosis and refers to unusual cells in the lobules of the breast. The lobules and acini of the terminal duct-lobular unit (TDLU), the basic functional unit of the breast, may become distorted and undergo expansion due to the abnormal proliferation of cells comprising the structure. These changes represent a spectrum of atypical epithelial lesions that are broadly referred to as lobular neoplasia (LN). One subset of LN can be defined as LCIS based on specific cellular traits and tissue changes seen histologically. These lesions are preceded by atypical lobular hyperplasia and may follow a linear progression to invasive lobular carcinoma (ILC), with specific genetic aberrations. This process coincides with the progression of ductal neoplasia to ductal carcinoma in situ and invasive carcinoma. Rarely, terminal ducts may be involved in lobular neoplasia, known as pagetoid spread. Many do not consider LCIS to be a true case of cancer, but it can indicate an increased risk of future cancer. In 2018, the eighth edition of the American Joint Committee on Cancer (AJCC) removed LCIS from tumor staging and considers it a benign entity. Cells of Lobular Neoplasia (LN), including both Atypical Lobular Hyperplasia and LCIS, and ILC share common genetic alterations, perhaps accounting, in part, for the similarities in histologic appearance. Classic LCIS and invasive lobular lesions are low-grade ER and PR-positive cancers, referring to the positive expression of Estrogen and Progesterone receptors on the neoplastic cells (determined via immunohistochemistry). These entities are also both classically negative for HER2 (human epidermal growth factor receptor 2). These hormone and growth factor receptors are clinically significant, as they represent targets for chemotherapy.