AXL and cancer: The impact of Axl signaling on solid tumor growth is well established; studies by our laboratory and others have shown that Axl targeting, either genetically or pharmacologically, significantly slows tumor progression in many cancer types, including head and neck [15,21], breast [26,44,45,46,47], ovarian [23,48], lung [49,50], pancreatic [24], bladder [26], colon [47], and skin cancer [51].