CLL exhibits differential apoptosis 48 hours after IR, which correlates with the presence of deletion of 17p, but also with the level of expression of miR-34a. Apoptosis was assessed by annexin/7-AAD staining 48 hours after IR in primary CLL cells (n = 35; graph shows mean and standard error). We compared the rate of cell death in the patient groups harboring a 17p deletion, CLL patients with low miR-34a expression but no deletion of 17p, and high miR-34a expression but no 17p deletion. We found significantly decreased apoptosis in the patients with 17p deletion (P < .001) or with low expression of miR-34a (P = .04), whereas the difference between 17p deletion and the group with low miR-34a expression was not significant.