In 2013, the United States Federal Drug Administration (FDA) granted accelerated approval of ibrutinib, an inhibitor of Bruton tyrosine-kinase (BTK) and the first-in-class B-cell receptor (BCR) signaling inhibitor for the therapy of relapsed mantle cell lymphoma (MCL), chronic lymphocytic leukemia (CLL), and Waldenström macroglobulinemia (WM) [31,32]. Here, BTK is linked to Waldenstrom macroglobulinemia.