In CLL cells, constitutive phosphorylation of phospholipase C-γ2 (PLC-γ2), spleen tyrosine kinase (Syk), protein kinase C (PKC)-β, BTK, and phosphoinositide 3′-kinase (PI3K) resulted in the activation of the nuclear factor kappa B (NF-κB) pathway [21]. Here, BTK is linked to B-cell chronic lymphocytic leukemia.