CXCR4 and B-cell chronic lymphocytic leukemia: Previous studies have demonstrated that activation of spleen tyrosine kinase (SYK) increases the risk of chemotherapy failure or relapse of B cell acute lymphoblastic leukemia (B-ALL) (Perova et al., 2014), and its inhibitors, PRT318 and P505-15, inhibited the survival and migration of chronic lymphocytic leukemia (CLL) by blocking the activation of chemokine receptors (CXCR4, CXCR5) and SYK (Hoellenriegel et al., 2012).