For that we treated primary CLL cells from 13 patients with 5 μM BTK inhibitor ibrutinib for 1 hour before co-culturing them for 48 hours which significantly impaired miR-21 upregulation, in further agreement with the involvement of the BCR signaling pathway in the regulation of miR-21 expression in CLL (Fig. 4e). This evidence concerns the gene BTK and B-cell chronic lymphocytic leukemia.