It plays a major role in proximal and distal BCR signaling events in CLL cells [67], and an available inhibitor, 4-amino-5-(4-phenoxyphenyl)-7H-pyrrolo[3,2-d]pyrimidin-7-yl-cyclopentane (Lck-i), is described to be highly selective in its ability to inhibit this SFK [173–175]. Here, BCR is linked to B-cell chronic lymphocytic leukemia.