We thus performed shRNA-mediated knockdown of Six1 in the highly metastatic 66Cl4 mouse mammary carcinoma cell line (Figure 5A), which expresses high levels of endogenous Six1 and metastasizes from the orthotopic site when injected into syngeneic immunocompetent BALB/c mice [37]. Here, SIX1 is linked to breast carcinoma.