BCL2 and B-cell chronic lymphocytic leukemia: For example, del13q-, the most common cytogenetic alteration in CLL [19], which causes the deletion of the genes encoding for the regulatory miR-15 and miR-16 and the consequent upregulation of bcl-2 expression [18], is present in only approximately 50% of CLL cases and not all the cells of the leukemic clones display this alteration.