BTK and B-cell chronic lymphocytic leukemia: Finally, and possibly most convincingly, inhibition of BCR signaling by blocking the action of Bruton’s tyrosine kinase (BTK) (26–29) or of phosphoinositide 3’ kinase delta (PI3Kδ) (30–33) has a very significant effect on CLL cell survival, growth, and trafficking (9, 34–38).