Indeed, various degrees of recombination of the foxed Trp53, Brca1, and Palb2 alleles were detected by PCR genotyping in available non-mammary tumors (Supplementary Fig. 2), indicating that the Wap-cre was indeed leaky and that at least some of those tumors might stem from the unintended gene ablation events. This evidence concerns the gene BRCA1 and breast cancer.