BTK and B-cell chronic lymphocytic leukemia: Remarkably, driving leukemic cells out of LN into PB induces death by deprivation of milieu-derived signals and is one of the modes of action (MOA) of a very efficient treatment option in CLL, ibrutinib, the first approved Bruton ́s tyrosine kinase (BTK) inhibitor with activities on multiple other kinases (73).