CX3CL1 and neoplasm: It has been shown in some tumor types that the membrane‐bound FKN can promote metastasis of CX3CR1+ circulating tumor cells towards tissues displaying a high CX3CL1 expression, such as bones, lungs, and nervous tissues (Shulby et al, 2004; Marchesi et al, 2008; Erreni et al, 2010; Gaudin et al, 2011; Jamieson‐Gladney et al, 2011; Kim et al, 2012; Marchica et al, 2019; Korbecki et al, 2020).