BTK and B-cell chronic lymphocytic leukemia: Targeting BTK in CLL and MCL with ibrutinib results in direct inhibition of cell proliferation and homing/migration due to disruption of BCR and chemokine receptor signaling (Herman et al., 2011; de Rooij et al., 2012; Ponader et al., 2012; Hendriks et al., 2014; Pal Singh et al., 2018).