In addition, the role of CXCL12 in the primary tumour in the establishment of organ-specific metastasis has been described: Cancer-associated fibroblasts in the primary tumour mimic the bone marrow microenvironment by producing CXCL12, which has been found to enrich breast cancer Src-hyperactive clones, which survive in the bone marrow (Zhang et al. 2013). This evidence concerns the gene SRC and breast cancer.