CXCR4 and breast cancer: Third, BMSC expression of Sdf1, a major cytokine promoting breast cancer cell migration, was unaffected by ISO treatment for 2, 6, or 24 h (Figure S3C); in breast cancer cells treated with ISO, the expression of RANK and CXCR4—the receptors for RANKL and SDF1, respectively—remained unchanged as well (Figure S3D,E).