Ibrutinib, a first-in-class, once-daily oral Bruton’s tyrosine kinase inhibitor (BTKi), is approved in Europe as monotherapy for the treatment of adults with chronic lymphocytic leukemia (CLL) and those with mantle cell lymphoma (MCL) who have received ≥ 1 prior line of therapy [1]. This evidence concerns the gene IBTK and B-cell chronic lymphocytic leukemia.