Ductal carcinoma in situ (DCIS), also known as intraductal carcinoma, is a pre-cancerous or non-invasive cancerous lesion of the breast. In this condition abnormal cells are found in the lining of one or more milk ducts in the breast. In situ means "in place" and refers to the fact that the abnormal cells have not moved out of the mammary duct and into any of the surrounding tissues in the breast (precancerous means that it has not yet become an invasive cancer). In some cases, DCIS may become invasive cancer and spread to other tissues, although it is not currently known how to predict which lesions will become invasive. DCIS encompasses a wide spectrum of diseases ranging from low-grade lesions that are not life-threatening to high-grade (i.e. potentially highly aggressive) lesions.