CXCR2 and breast cancer: Organotypic microfluidic assays have shown that breast cancer cells do not exhibit extravasation dynamics into the muscle microenvironment, but do so into bone, through the interplay of breast cancer cell receptor CXCR2 and the chemokine CXCL5 secreted by the bone (Bersini et al., 2014; Jeon et al., 2015).