Recently, it was also described that the ectopic expression of (DLK2) EGFL9 significantly promotes cell migration and invasion in mammary epithelial cell lines and cancer metastasis in vivo, while a knockdown of DLK2 in highly metastatic breast cancer cell lines decreased cell migration and invasion and inhibited distant tumor metastasis in vivo [16]. This evidence concerns the gene DLK2 and breast cancer.