To identify genes involved in initiation or progression of BC, we performed SB transposon-based screens in mammary glands from eight different genetically engineered mouse model (GEMM) strains, each selected on the basis of activation of genes/pathways thought to promote BC (Pik3caE545K, Pik3caH1047R, Trp53LSL-R270H, KrasG12D, Notch1ICD, Elf3, and Stat3C) or deletion of tumor suppressor genes which inhibit it (Lfng) (Supplementary Table 1). This evidence concerns the gene ELF3 and breast cancer.