BTK is a critical kinase in the B-cell receptor (BCR) pathway that drives BCR signaling cascade leading to activation of downstream NF-κB and phosphatidylinositol-3-kinase (PI3K) pro-survival pathways in CLL, indolent forms of NHL, and ABC-DLBCL5. The gene discussed is BCR; the disease is B-cell chronic lymphocytic leukemia.