Figure 1.

Classic linear multi-step model of human breast cancer progression based on histomorphological and epidemiological data. Molecular alterations occurring in breast epithelium of a normal terminal duct lobular unit result in atypical ductal hyperplasia (ADH), the earliest neoplastic stage of progression. Subsequent molecular alterations occur in ADH, resulting in ductal carcinoma in situ (DCIS), another early neoplastic stage, upon which additional events occur, resulting in invasive ductal carcinoma (IDC).