CLL exhibits differential miR-34a expression based on genetic background. Relative expression levels of miR-34a are shown in cases stratified by genomic aberrations and TP53 mutation without (■) and with IR (▲). CLL cases with a deletion of 17p show a severely reduced level of miR-34a expression with and without IR. Similarly, cases with TP53 mutation but no 17p deletion showed failure to up-regulate miR-34a after IR. The 2 cases with “normal” up-regulation had a wild-type TP53 allele in 50% to 70% of cells (* case with 70% wild-type allele [c.455C > T], ** case with 50% wild-type allele [c.847C > T]), likely explaining the up-regulation of miR-34a after IR. Cases with 11q deletion did not show different basal expression or induction compared with cells without 17p-, 11q-, or TP53 mutation.