To investigate this possibility, the biological activity of stromal SDF‐1 was evaluated employing the Boyden chamber cell migration assay using human breast cancer MDA‐MB‐231 cells and DCIS cells overexpressing CXCR4 (DCIS‐CXCR4) (Figure 5E). Here, CXCR4 is linked to ductal breast carcinoma in situ.