For example, in CLL, the importance of the BCR pathway was already emphasized prior to the clinical use of BTKi (24), whereas in mantle cell lymphoma (MCL) and Waldenström’s macroglobulinemia (WM) the dependence of the malignant B cells on BCR and/or BTK was mostly discovered later (25, 26). Here, BCR is linked to B-cell chronic lymphocytic leukemia.