CX3CR1 and neoplasm: Chemokine axes, such as fractalkine (CX3CL1)/CX3CR1, C-X-C motif chemokine ligand 12 (CXCL12)/C-X-C chemokine receptor type 4 and 7(CXCR4/CXCR7), CCL2/CCR2, and CCL5/CCR5, are clearly involved in tumor progression (Held-Feindt et al., 2010; Hattermann and Mentlein, 2014; Laudati et al., 2017).