Fitamant et al. showed that the downregulation of netrin-1 by siRNA or the inhibition of netrin-1/dependence receptor interaction is able to promote apoptosis in tumor cell lines and prevent metastasis in both a mammary cancer cell line mouse model of lung colonization and lung metastasis-xenograft model of human breast cancer, but this reduction in metastasis was restricted to breast cancer cell lines or tumors expressing high levels of netrin-1 [14]. Here, NTN1 is linked to breast cancer.