CXCR4 and breast cancer: Among the genes that showed at least a 0.25 log2 fold change upon insulin treatment respect to vehicle and the reduction of this increase in the presence of metformin, we focused on the C-X-C Motif Chemokine Receptor 4 (CXCR4) due to its acknowledged role as prognostic marker and main driver of BC metastasis [51–53].