AXL and breast cancer: AXL has been implicated in epithelial-mesenchymal transition (EMT) and has been hypothesized to play a key role not only in development of metastasis, but also in resistance to chemotherapy and targeted therapies, including lapatinib resistance in HER2-positive breast cancer [43] and in erlotinib resistance in EGFR-mutant non-small-cell lung cancer [44].