CX3CR1 and cancer: Fractalkine, the sole member of the CX3C chemokine family, can function as a chemoattractant for monocytes, NK, mast cells, T cells, and B cells expressing the CX3CR1 [55, 56], and although the CX3CL/CX3CR1 signaling axis is involved in normal immune regulation, dysregulation of CX3CR1 signaling has also been found to be associated with variety of human cancers [28].