CXCR4 and breast cancer: In order to analyze the proliferative effects induced by CXCR4 activation, the obtained mammary carcinoma primary cultures were starved for 24 h and treated with 25 nM SDF-1 for further 24 h (the concentration was chosen as the maximal growth stimulatory effect obtained in previous experiments on human breast cancer cell lines [19]), and then MTT cell viability assays were performed.