13q deletion anatomy and disease progression in patients with chronic lymphocytic leukemia

Historically, genes targeted by recurrent chromosomal deletions have been identified within the smallest genomic region shared in all patients, the minimally deleted region (MDR). However, deletions this small do not occur in all patients and are a simplification of the impact larger heterogeneous deletions have during carcinogenesis. We use the example of 13q14 deletions in chronic lymphocytic leukemia to show that genes outside MDRs are associated with disease progression. Genomic profiling of 224 patients identified 205 copy number alterations on chromosome 13 in 132 cases. Deletions including DLEU2 were heterogeneous (845 Kb-96.2 Mb) and identified two breakpoint cluster regions within short interspersed nuclear elements proximal to DLEU2 and within long interspersed nuclear elements/L1 repeats distal to GUCY1B2. After defining a deletion class on the basis of size and location, we show that (a) at diagnosis, larger deletions (class II) were associated with a significantly increased risk of disease progression (odds ratio = 12.3; P = 0.005), (b) in progressive patients, class II deletions were enriched (P = 0.02) and (c) this association was independent of IgVH mutational status, ZAP70 expression and ATM/TP53 deletion. Deletion of a 1Mb gene cluster (48.2-49.2 Mb), including SETDB2, PHF11 and RCBTB1, was significantly associated (P < 0.01) with disease progression. Here, we show that the deletion of genes outside MDRs can influence clinical outcome. Leukemia (2011) 25, 489-497; doi:10.1038/leu.2010.288; published online 10 December 2010