In our recent publication of somatic genomic editing in mice, we used intraductal injection of AAV to edit Kras to KrasG12D and generated mammary tumors that are characterized as ER-/PR- ductal carcinoma with widespread and extensive squamous differentiation6, histologically similar to the mouse tumors induced by intraductal injection of lenti-HrasQ61L6. Here, ESR1 is linked to breast cancer.