CXCL12 and breast cancer: Cochrane’s Q test did not provide evidence of heterogeneity between CCL1 (p = 0.227), CCL2 (p = 0.982), CCL18 (p = 0.221), CXCL5 (p = 0.533), CXCL12 (p = 0.977), and CXCL13 (p = 0.520) and breast cancer.