Using the Cas9 transgenic mouse line, we further examined the direct effect of TS deficiency on metastatic colonization using the experimental metastasis model (tail vein injection) of TSAE1 tumor cells that carry a P53 homozygous hotspot point mutation G809A (R270H) (Fig. S3C) and Her2 overexpression (Fig. 3G, H, Fig. S3D), two well-recognized breast cancer etiology factors. Here, ERBB2 is linked to breast cancer.