A comprehensive evaluation of the prognostic significance of 13q deletions in patients with B-chronic lymphocytic leukaemia

Importance of immunoglobulin heavy chain variable region mutational status in del(13q) chronic lymphocytic leukemia

Among prognostic factors for chronic lymphocytic leukemia (CLL), immunoglobulin heavy chain variable region (IGHV) mutation status and DNA analysis appear to be the most important. However, there is limited clinical outcome information for patients with the favorable-risk del(13q) and poor-risk unmutated IGHV. We retrospectively screened all patients with CLL at our institution between 2004 and June 2010 for del(13q) who also had an IGHV analysis. Unmutated IGHV was found in 38/79 patients; age, Rai stage, prior therapy, and time to evaluation were similar to those for patients with mutated IGHV. Unmutated patients were nearly four times more likely to harbor additional chromosomal aberrations compared to mutated patients (p < 0.001). During a median follow-up of 4.5 years, unmutated patients were more likely to demonstrate Rai stage progression (69% vs. 31%, log-rank p < 0.001) and to receive treatment (5-year cumulative probability of treatment: 65% vs. 32%, p < 0.001). Patients with unmutated CLL also had a shorter overall survival (5-year survival probability: 72% vs. 100%, p < 0.001). When limiting analysis to the 47 patients with del(13q) as a sole chromosomal abnormality, the 13 (28%) unmutated patients were more likely to demonstrate Rai progression (p < 0.001), to receive treatment (p = 0.02), and to have a shorter overall survival (p = 0.13) than the 34 mutated patients. These data suggest that del(13q) conveys an indolent course only in patients with IGHV-mutated CLL.

The prognostic significance of various 13q14 deletions in chronic lymphocytic leukemia

PURPOSE

To further our understanding of the biology and prognostic significance of various chromosomal 13q14 deletions in chronic lymphocytic leukemia (CLL).

EXPERIMENTAL DESIGN

We analyzed data from SNP 6.0 arrays to define the anatomy of various 13q14 deletions in a cohort of 255 CLL patients and have correlated two subsets of 13q14 deletions (type I exclusive of RB1 and type II inclusive of RB1) with patient survival. Furthermore, we measured the expression of the 13q14-resident microRNAs by quantitative PCR (Q-PCR) in 242 CLL patients and subsequently assessed their prognostic significance. We sequenced all coding exons of RB1 in patients with monoallelic RB1 deletion and have sequenced the 13q14-resident miR locus in all patients.

RESULTS

Large 13q14 (type II) deletions were detected in approximately 20% of all CLL patients and were associated with shortened survival. A strong association between 13q14 type II deletions and elevated genomic complexity, as measured through CLL-FISH or SNP 6.0 array profiling, was identified, suggesting that these lesions may contribute to CLL disease evolution through genomic destabilization. Sequence and copy number analysis of the RB1 gene identified a small CLL subset that is RB1 null. Finally, neither the expression levels of the 13q14-resident microRNAs nor the degree of 13q14 deletion, as measured through SNP 6.0 array-based copy number analysis, had significant prognostic importance.

CONCLUSIONS

Our data suggest that the clinical course of CLL is accelerated in patients with large (type II) 13q14 deletions that span the RB1 gene, therefore justifying routine identification of 13q14 subtypes in CLL management.

13q14 deletion size and number of deleted cells both influence prognosis in chronic lymphocytic leukemia

Deletion at 13q14 is detected by fluorescence in situ hybridization (FISH) in about 50% of chronic lymphocytic leukemia (CLL). Although CLL with 13q deletion as the sole cytogenetic abnormality (del13q-only) usually have good prognosis, more aggressive clinical courses are documented for del13q-only CLL carrying higher percentages of 13q deleted nuclei. Moreover, deletion at 13q of different sizes have been described, whose prognostic significance is still unknown. In a multi-institutional cohort of 342 del13q-only cases and in a consecutive unselected cohort of 265 CLL, we investigated the prognostic significance of 13q deletion, using the 13q FISH probes locus-specific identifier (LSI)-D13S319 and LSI-RB1 that detect the DLEU2/MIR15A/MIR16-1 and RB1 loci, respectively. Results indicated that both percentage of deleted nuclei and presence of larger deletions involving the RB1 locus cooperated to refine the prognosis of del13q-only cases. In particular, CLL carrying <70% of 13q deleted nuclei with deletions not comprising the RB1 locus were characterized by particularly long time-to-treatment. Conversely, CLL with 13q deletion in <70% of nuclei but involving the RB1 locus, or CLL carrying 13q deletion in ≥70% of nuclei, with or without RB1 deletions, collectively experienced shorter time-to-treatment. A revised flowchart for the prognostic FISH assessment of del13q-only CLL, implying the usage of both 13q probes, is proposed.

Standardization of fluorescence in situ hybridization studies on chronic lymphocytic leukemia (CLL) blood and marrow cells by the CLL Research Consortium

Five laboratories in the Chronic Lymphocytic Leukemia (CLL) Research Consortium (CRC) investigated standardizing and pooling of fluorescence in situ hybridization (FISH) results as a collaborative research project. This investigation used fixed bone marrow and blood cells available from previous conventional cytogenetic or FISH studies in two pilot studies, a one-day workshop, and proficiency test. Multiple FISH probe strategies were used to detect 6q-, 11q-, +12, 13q-, 17p-, and IGH rearrangements. Ten specimens were studied by participants who used their own probes (pilot study 1). Of 312 FISH interpretations, 224 (72%) were true-negative, 74 (24%) true-positive, 6 (2%) false-negative, and 8 (3%) false-positive. In pilot study no. 2, each participant studied two specimens using identical FISH probe sets to control for variation due to probe sets and probe strategies. Of 80 FISH interpretations, no false interpretations were identified. At a subsequent workshop, discussions produced agreement on scoring criteria. The proficiency test that followed produced no false-negative results and 4% (3/68) false-positive interpretations. Interpretation disagreements among laboratories were primarily attributable to inadequate normal cutoffs, inconsistent scoring criteria, and the use of different FISH probe strategies. Collaborative organizations that use pooled FISH results may wish to impose more conservative empiric normal cutoff values or use an equivocal range between the normal cutoff and the abnormal reference range to eliminate false-positive interpretations. False-negative results will still occur, and would be expected in low-percentage positive cases; these would likely have less clinical significance than false positive results. Individual laboratories can help by closely following rigorous quality assurance guidelines to ensure accurate and consistent FISH studies in their clinical practice and research.

The basis and rational use of molecular genetic testing in mature B-cell lymphomas

An increasing number of neoplasms are associated with variably specific genetic abnormalities. This is best exemplified by hematological malignancies, in which there is a growing list of entities that are defined by their genetic lesion(s); this is not (yet) the case in mature B-cell lymphomas. However, enhanced insights into the pathogenesis of this large and diverse group of lymphomas have emerged with the ongoing unraveling of a plethora of fascinating genetic abnormalities. The purpose of this review is to synthesize well-recognized data and nascent discoveries in our understanding of the genetic basis of a spectrum of mature B-cell lymphomas, and how this may be applied to contemporary clinical practice. Despite the explosion of new and exciting knowledge in this arena, with the potential for enhanced diagnostic and prognostic strategies, it is essential to remain cognizant of the limitations (and complexity) of genetic investigations, so that assays can be developed and used both judiciously and rationally.