Given that CXCL12 can stimulate or repress cell motility in a dose-dependent manner in monocytic leukemia and colon cancer cell lines [18,50], we wanted to determine the CXCL12 concentration that is optimal for stimulating CXCR4-mediated motility in LNCaP cells. The gene discussed is CXCL12; the disease is monocytic leukemia.