Lobular carcinoma-in-situ (LCIS) is usually an incidental finding most commonly seen in upper outer and upper inner quadrants. It is multicentric in about 70% of cases and bilateral in 30% to 40% of cases. The lobules are expanded and completely filled by a uniform population of round, small to medium-sized tumor cells. However, lobular enlargement and the complete absence of lumens are not absolute diagnostic requirements. Atypia, nuclear pleomorphism, mitotic activity and necrosis are usually absent – except in a small subset of cases called Pleomorphic LCIS. The tumor cells show loss of cohesion. Scattered signet ring cells are frequently present. The tumor cells may show pagetoid spread into the neighboring terminal ducts; however, Paget disease is almost never seen. Stains for mucin are positive in about 75% of LCIS cases. Immunohistochemically, the lack of E-Cadherin and beta-catenin and positivity for high molecular weight cytokeratin (perinuclear pattern) in LCIS help distinguish it from DCIS. LCIS as a Risk Factor: About 20% to 30% of LCIS patients will develop invasive breast cancer which may be either lobular or ductal type. The risk is greater in cases with well-developed LCIS lesions. The risk is not dependent upon the quantity of LCIS. The increased risk applies to both breasts. The patients with LCIS may be safely followed. Therapeutic intervention (such as simple mastectomy) may be considered in patients with strong family history of breast cancer, apprehensive patients, or in patients with extensive fibrocystic disease.