CXCR4 and B-cell chronic lymphocytic leukemia: The critical role of CXCR4 for tumor progression has already been known from O’Hayre et al., who examined the CXCL12/CXCR4 signaling network in chronic lymphatic leukemia (CLL) in 2010 but due to technical limitations, this work lacked comprehensive phosphosite analysis [121].