It is important to remark that anti-tumor properties have been described for sFKN, while, in some cancers, it has been shown that membrane-bound FKN promotes metastasis of CX3CR1+ cancer cells towards sites with elevated CX3CL1 expression, such as lungs, bones, and others [41,45,92,99,130,131,132,133]. This evidence concerns the gene CX3CR1 and cancer.