BTK and B-cell chronic lymphocytic leukemia: In a similar way, overexpression and constitutive phosphorylation of BTK lead to the activation of phospholipase C-γ2 (PLCG2), and of extracellular signal-regulated kinase (ERK) and nuclear factor kappa-beta, which promote upregulation of pro-survival signals and migration of chronic lymphocytic leukemia (CLL) cells [12, 13].