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By Mayo Clinic staffInvasive lobular carcinoma starts when cells in one or more milk-producing glands of the breast start growing abnormally. The cells divide more rapidly than normal cells do. When these abnormal cells stay within the lobule, the condition is referred to as lobular carcinoma in situ (LCIS) and is considered a marker for increased risk of breast cancer. At some point, abnormal cells may break out of the lobules and invade or "infiltrate" the surrounding tissue, becoming ILC.
About half the lobular breast cancers involve alterations (mutations) in a gene called E-cadherin (CDH1). This gene controls the activity of a protein that helps keep tumor cells from invading normal tissue and spreading. Some scientists believe that the turning off of E-cadherin sets the stage for ILC to develop. When lobular carcinoma is diagnosed, a laboratory doctor (pathologist) may order an E-cadherin protein study on the tissue to help differentiate ILC from LCIS.