RB1 and neoplasm: To avoid a bias toward induction of genetic events in a specific mammary cell type and to control the timing of tumor initiation, we induced Brca1 loss, inhibition of proteins of the Rb family (Rbf), and Trp53 loss in the mammary ductal epithelium by injecting adenovirus expressing Cre recombinase into the mammary ducts of adult mice.