The SV40 large T-antigen (Tag) is an efficient inducer of tumor formation; this is achieved by inactivation of tumor suppressor proteins such as p53 and retinoblastoma protein.242 Tag overexpression can lead to formation of breast and prostate cancers that histologically resemble the diseases found in humans.243 Similar to the MMTV-PyMT model, the C3(1)/Tag model can mimic human DCIS progression in mice. Here, TP53 is linked to ductal breast carcinoma in situ.