For example, Axl is upregulated by Slug and Snail in MCF10A immortalized breast epithelial cells and plays a critical role in breast cancer cell invasion [26], and Slug induces the expression of Axl among 49 receptor tyrosine kinases at the transcriptional level to activate Axl, which maintains Slug expression through a positive feedback loop [28]. Here, AXL is linked to breast cancer.