Ibrutinib, a first-in-class, oral, once-daily, Bruton’s tyrosine kinase (BTK) inhibitor, has been demonstrated as an effective treatment for chronic lymphocytic leukemia (CLL), mantle cell lymphoma (MCL), Waldenström macroglobulinemia (WM), marginal zone lymphoma and chronic graft versus host disease (Treon et al., 2015; Chanan-Khan et al., 2016; Miklos et al., 2017; Dimopoulos et al., 2018; Burger et al., 2019; Byrd et al., 2019; Moreno et al., 2019; Shanafelt et al., 2019). This evidence concerns the gene BTK and B-cell chronic lymphocytic leukemia.