Next, we investigated whether the BTK inhibitor ibrutinib, an agent interfering with microenvironmental interactions in CLL [29], might modulate the function of the calcitriol/VDR system by assessing VDR and CYP24A1 expression in 12 CLL patients under ibrutinib treatment. This evidence concerns the gene CYP24A1 and B-cell chronic lymphocytic leukemia.