Ductal carcinoma in situ, or DCIS, is a form of pre-cancer in which a carcinoma, or abnormal growth of cells, is found in the lining of a breast duct. "In situ" means that the abnormal cells have not spread or invaded other breast tissues outside of the duct. In other words, DCIS is considered noninvasive. However, in some cases, DCIS can become a more aggressive form of cancer called invasive ductal carcinoma, or IDC.
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Although DCIS is not usually detected during a breast physical exam, the frequency of the diagnosis of DCIS has increased dramatically in recent years, as the use of screening mammography has become more common. There is an extremely high cure rate when DCIS is detected early. In fact, deaths from DCIS as well as other types of breast cancer have been declining in recent years due to earlier detection and treatment.