Although about a quarter of human breast cancers have p53 mutations, the utility of this model is that Trp53 null mouse mammary tissue develops normally until about 8 months of age, when both ductal carcinoma in situ and aneuploidy are evident, thus reproducing the long latency and early instability observed in most human breast cancers. The gene discussed is TP53; the disease is ductal breast carcinoma in situ.