We used MMTV-HER2 mice as a murine model of breast cancer since these show slow progression from early lesions such as hyperplasia and mammary intra-epithelial neoplasia (Fig. 1a, b, Supplementary Table 1), the latter a similar lesion to DCIS27, to invasive tumors (Fig. 1c, Supplementary Table 1). Here, ERBB2 is linked to breast cancer.