In adult normal cells, such as normal brain tissue, hippocampus, heart and liver, AXL expression is relatively low (27, 28), but AXL levels are abnormally high in many human cancers, including non-small cell lung cancer (NSCLC), esophageal cancer, glioblastoma, breast cancer and chronic lymphocytic leukemia (29–40), which is associated with reduced overall survival and enhanced disease progression. Here, AXL is linked to cancer.