The signaling pathway mediated by the B-cell receptor (BCR) and its constituent, Bruton’s tyrosine kinase (BTK), is implicated in the pathogenesis of various B-cell malignancies, such as CLL, mantle cell lymphoma (MCL), and diffuse large B-cell lymphoma (DLBCL) [97]. The gene discussed is BTK; the disease is B-cell chronic lymphocytic leukemia.