Since CXCR4+CXCR7+ (double positive), and two single positive subpopulations, i.e. CXCR4+CXCR7− and CXCR4−CXCR7+, are present in all GBM cell lines we studied, it is possible that in GBM, CXCR7 and CXCR4 not only activate their own distinct signaling pathways, but also interact with each other to create a diverse response to CXCL12 stimulation. The gene discussed is CXCL12; the disease is glioblastoma.