Mammary tumors developed in p16mt;Brca1MGKO mice expressed 44% Gata3, and 54% Elf5, both of which are genes associated with luminal cell differentiation, relative to the tumor-free mammary tissues of the same mouse (Supplementary Figure S2D), confirming Brca1-deficiency impaired luminal differentiation during tumorigenesis, as we previously demonstrated [24, 25]. Here, ELF5 is linked to breast cancer.