Trisomy 12 and structural abnormalities of 13q14 occurring in the same clone in chronic lymphocytic leukaemia

Genomic instability in a chronic lymphocytic leukemia patient with mono-allelic deletion of the DLEU and RB1 genes

Background

The most frequent cytogenetic abnormality detected in chronic lymphocytic leukemia (CLL) patients is the presence of a deletion within the chromosome band 13q14. Deletions can be heterogeneous in size, generally encompassing the DLEU1 and DLEU2 genes (minimal deleted region), but at times also including the RB1 gene. The latter, larger type of deletions are associated with worse prognosis.

Genomic instability is a characteristic of most cancers and it has been observed in CLL patients mainly associated with telomere shortening.

Case presentation

Cytogenetic and fluorescence in situ hybridization studies of a CLL patient showed a chromosomal translocation t(12;13)(q15;q14), a mono-allelic 13q14 deletion encompassing both the DLEU and RB1 genes, and genomic instability manifested as chromosomal breaks, telomeric associations, binucleated cells, nucleoplasmic bridges, and micronucleated cells.

In conclusion, our CLL patient showed genomic instability in conjunction with a 13q14 deletion of approximately 2.6 megabase pair involving the DLEU and RB1 genes, as well as other genes with potential for producing genomic instability due to haploinsufficiency.

Coexistence of trisomy 12 and del(13)(q14.3) in two patients with chronic lymphocytic leukemia

We describe two patients with diagnosis of chronic lymphocytic leukemia (CLL) in whom interphase fluo?rescence in situ hybridization (FISH) analysis revealed trisomy 12 and del(13)(q14.3) occurring in the same clone. These abnormalities are rarely seen together and the prognostic relevance of their coexistence is still unclear. According to some data, a probable adverse prognosis for this group of patients is suggested. Our patients have been in a stable phase of the disease for more than one year since the given abnormalities were documented in their karyotypes. Further study is necessary to determine the prognostic significance of coexistence of these abnormalities in CLL patients.

Cytogenetic characterisation in Chinese patients with chronic lymphocytic leukemia: a prospective, multicenter study on 143 cases analysed with interphase fluorescence in situ hybridisation

Chronic lymphocytic leukemia (CLL) is infrequent in Chinese people. Conventional cytogenetic analysis underestimates the frequency of chromosome aberrations in CLL due to the low rate of spontaneous mitoses. The aim of this study was to prospectively explore the frequency of chromosomal abnormalities in Chinese patients with CLL using interphase fluorescence in situ hybridisation (FISH) and probes for 12 centromere, 13q14, 14q32, 17p13, 11q22 and 6q23 on 143 patients with CLL. Molecular cytogenetic aberrations were found in 104 patients (72.7%) and 40 patients (28.0%) with more than two abnormalities. The most frequent abnormality was del(13q14) (47.6%), followed by trisomy 12 (21.7%), 14q32 translocation (19.6%), del(17p13) (12.6%), del(11q22) (11.9%) and del(6q23) (4.9%), respectively. The percentages of patients with aberrations by FISH were 75.4%, 72.3% and 67.7% for Binet stages A, B and C, respectively. In early stage (Binet A), del(13q14) aberration was more frequent than in Binet B and C (61.5% vs. 31.9% and 41.9%) (P=0.021). Patients with advanced stage (Binet C) had more frequent del(17p13) aberration than in Binet A and B (32.3% vs. 9.2% and 4.3%) (P=0.008). It was showed that the frequencies of the chromosomal abnormalities in our study population were similar to the frequencies in Western countries.

Trisomy 8 as sole cytogenetic abnormality in a case of chronic lymphocytic leukemia

A 49-year-old man, who had been diagnosed with chronic lymphocytic leukemia (CLL) in 2002, had a normal karyotype in his bone marrow. Trisomy 8 was demonstrated in his peripheral blood in 2005. Fluorescence in situ hybridization using an LSI CEP 8 probe performed on the archival bone marrow specimen showed three hybridization signals in 40% of 200 interphase cells scored. This confirmed that the trisomy 8 abnormality was present in both the blood and bone marrow samples. Trisomy 8 as the sole chromosomal abnormality in CLL is a very rare finding. The prognostic significance of trisomy 8 in CLL remains to be seen.

Clinical, immunophenotypic, and molecular profiling of trisomy 12 in chronic lymphocytic leukemia and comparison with other karyotypic subgroups defined by cytogenetic analysis

In a cohort of 130 unselected chronic lymphocytic leukemia (CLL) patients, 73 cases had normal karyotypes, 57 cases had abnormal karyotypes, and 22/57 cases carried more than one abnormality. Trisomy 12 (+12) was the most common abnormality (26/130 cases; 20%), and 17/26 cases had isolated +12. Del(13q)/t13q/-13 was detected in 19/130 cases (14.6%), and 5/19 cases had isolated del(13)(q12q14). Deletion (11)(q23) and del(17p)/-17 were detected in 5/130 cases, respectively. CD38 expression was significantly more frequent in the +12/11q/17p versus the normal/del(13q) subgroups. A significant association was detected between +12 and FMC7 positivity. IGHV-unmutated cases were significantly more frequent in the +12/11q/17p subgroups. Patients with normal karyotype/del(13q) had a longer median time to progression versus the patients in the +12/11q/17p subgroups. According to multivariate analysis, only IGHV mutation status remained a statistically significant variable for progression-free survival (PFS). Furthermore, IGHV mutation status and clinical stage at diagnosis were the only significant prognostic factors for overall survival. Among Binet-A patients, significant parameters for shorter PFS were +12 or 11q/17p aberrations, CD38 expression, and IGHV unmutated status. In multivariate analysis, only CD38 expression and IGHV-unmutated status retained statistical significance for PFS. In conclusion, trisomy 12 in CLL is characterized by considerable heterogeneity and seems to be associated with disease progression.

Korean patients with chronic lymphocytic leukemia show the similar types of chromosomal aberrations as those in Europe and North America

Chronic lymphocytic leukemia (CLL) is frequent in the West, but rare in Korea. In this study, the frequency of chromosome aberration in Korean CLL patients was examined by applying interphase fluorescence in situ hybridization (FISH). Conventional cytogenetic test and FISH were performed on bone marrow aspirates obtained from 16 CLL patients. By applying DNA probes (Vysis, Downers Grove, IL, USA), the deletion in 11q22-23, 13q14, 13q34, and 17p13, and trisomy 12 were examined. With FISH, molecular cytogenetic aberration was detected in 10 of 16 patients [63%, 95% confidence interval (CI) 39-86], whereas with conventional cytogenetic test, chromosomal aberration was detected only in 2 out of 13 cases (15%, 95% CI 0-35). In total, the cases with one or more chromosomal aberrations were 11 out of 16 cases (69%, 95% CI 46-92). The most frequently detected aberration was the 13q14 deletion (69%, 95% CI 44-94), followed by trisomy 12 (19%, 95% CI 0-38) and 11q22 deletion (14%, 95% CI 0-33). No deletion in 17p13 was observed. In conclusion, CLL in Korean is a heterogeneous genetic disorder, showing similar genetic changes in Europe and North America.

Interphase cytogenetic analysis in Argentinean B-cell chronic lymphocytic leukemia patients: association of trisomy 12 and del(13q14)

We have evaluated genomic aberrations by conventional cytogenetics and fluorescence in situ hybridization (FISH) analysis in a series of 57 Argentinean B-cell chronic lymphocytic leukemia (B-CLL) patients. The studies were performed on stimulated peripheral blood lymphocytes. FISH analysis for trisomy 12, 13q14 deletion, and monosomy of TP53 (also known as p53) was performed according to standard protocols. Our results showed 46.3% of patients with clonal chromosomal alterations by conventional cytogenetics and 80.7% by FISH. Trisomy 12 was found in 21.9% of patients by G-banding analysis and in 35% by FISH studies. Allelic loss of 13q14 was observed in 63.2% patients, most of them showing D13S319 and D13S25 deletion; 11% of patients showed TP53 monosomy. Coexistence of trisomy 12 and 13q14 deletion was found in 17.5% of patients. In this group, deletion 13q14 was the prevalent clone, with percentages 25-35% higher than those observed for trisomy 12, suggesting clonal evolution. The coexistence of trisomy 12 with deletion 13q14 was observed in a higher frequency than reported in the literature. A probable adverse prognosis is suggested for this group of patients, likely related to clonal evolution.

Genetic imbalances in progressed B-cell chronic lymphocytic leukemia and transformed large-cell lymphoma (Richter's syndrome)

Chromosomal imbalances were examined by comparative genomic hybridization in 30 cases of B-cell chronic lymphocytic leukemia (CLL) at diagnosis, in sequential samples from 17 of these patients, and in 6 large B-cell lymphomas transformed from CLL [Richter's syndrome (RS)] with no available previous sample. The most common imbalances in CLL at diagnosis were gains in chromosome 12 (30%), and losses in chromosomes 13 (17%), 17p (17%), 8p (7%), 11q (7%), and 14q (7%). The analysis of sequential samples showed an increased number of chromosomal imbalances in 6 of 10 (60%) patients with clinical progression and in 2 patients with stable stage C disease. No karyotypic evolution was observed in four cases with stable stage A disease and in one RS clonally unrelated to the previous CLL. Gains of 2pter, and 7pter, and losses of 8p, 11q, and 17p were recurrent alterations associated with karyotype progression. RS showed a higher number of gains, losses, total alterations, and losses of 8p and chromosome 9 than CLL at diagnosis. 17p losses were associated with p53 gene mutations and with a significantly higher number of chromosomal imbalances than tumors with normal chromosome 17 profile. However, no relationship was observed between 9p deletions and p16(INK4a) gene alterations. Losses of 17p and an increased number of losses at diagnosis were significantly associated with a shorter survival. These findings indicate that CLL has frequent chromosomal imbalances, which may increase during the progression of the disease and transformation into large cell lymphoma. Genetic alterations detected by comparative genomic hybridization may also be of prognostic significance.

Disruption of the IFN-gamma cytokine network in chronic lymphocytic leukemia contributes to resistance of leukemic B cells to apoptosis

Recent evidence indicates that the slowly expanding population of CD5+ B cells that characterizes chronic lymphocytic leukemia (CLL) results primarily from defects in responses to cytokines that regulate apoptosis (e.g. I1-4, TGF-beta, IFN-alpha, IFN-gamma). We have now demonstrated not only that the enhanced anti-apoptotic effect of IFN-gamma on these neoplastic B cells is apparently mediated through increased levels of IFN-gamma receptors but also that there are increased numbers of IFN-gamma-expressing CD4 and CD8 T cells in these patients. This is the strongest evidence to date that multiple alterations in the IFN-gamma cytokine network contribute to the pathogenesis of CLL.

Update on the biology of chronic lymphocytic leukemia

An understanding of the molecular biology of B-cell chronic lymphocytic leukemia (B-CLL) has led to the appreciation that several different B-cell diseases are represented under this name. Variability in the bcl-2 family of proteins, p53 mutation, or the presence of various chromosomal abnormalities corresponds to variability of the clinical course of disease and response to therapy. Differential expression of cell surface adhesion molecules by B-CLL cells have also been shown to influence clinical outcome, as have the expression of immune regulatory molecules (eg, CD80, CD40R, CD27 and CD79b). Recent work studying immunoglobulin-heavy chain gene rearrangement postulates at least two subsets of B-CLL originating from different stages of B-cell development and following different clinical courses. The knowledge that B-CLL is the final consequence of many different molecular perturbations may allow the development of chemotherapies, immunotherapies, and gene therapies that target the specific molecular defect in a given case of B-CLL.

The prognostic significance of 13q14 deletions in chronic lymphocytic leukemia

Although chronic lymphocytic leukemia (CLL) is the most common leukemia in adults, little is known about the molecular abnormalities underlying it and their prognostic significance. Using a battery of six microsatellite markers from 13q12.3-14.3 between BRACA2 gene and the Rb gene, we assayed loss of heterozygosity (LOH) in 78 CLL patients. We found deletion in 13q14 in 29 patients (37%) between D13S153 and the AFMa 301wb5. Classical cytogenetics was less sensitive, as it detected the 13q14 deletion in only one out of 69 patients (1%) in whom adequate metaphases were obtained. We found no significant difference in survival between patients with and patients without 13q14 LOH. In subset of patients with low beta2-microglobulin levels, those with 13q14 LOH had significantly shorter survival than did patients with low beta2-microglobulin levels but no 13q14 LOH. Also patients in early Rai stages (0-II) with 13q14 LOH had shorter survival period (P = 0.05) than did patients without LOH. These data confirm the prevalence of 13q14 deletion in CLL and suggest that this deletion may help identify more aggressive disease in patients presenting with early stage disease.

The concept of typical and atypical chronic lymphocytic leukaemia

Subdivision of CLL into typical and atypical subtypes, as proposed by the FAB group in 1989, is not yet widely accepted and its clinical significance is still debated. In recent years, however, a strong correlation was found between atypical morphology trisomy 12 and an aberrant immunophenotype. In the first part of this review we discuss current concepts and generally accepted data on morphology, immunophenotype, genetic abnormalities, clinical features and prognostic factors in CLL. Subsequently, based on our own series and other recently published data, we analyse the validity and clinical impact of classifying CLL into typical and atypical entities and demonstrate that they may represent two closely related but different entities.

Association and clonal distribution of trisomy 12 and 13q14 deletions in chronic lymphocytic leukaemia

The coexistence of trisomy 12 and deletions of chromosome 13 (13q12-q32) has rarely been observed in chronic lymphocytic leukaemia (CLL). Fluorescence in situ hybridization (FISH) performed on 600 consecutive CLL patients revealed the association of trisomy 12 and 13q14 deletion, of at least one of the three markers analysed (RB1, D13S319 and D13S25), in 55 cases (9% of 600 and 46% of 120 trisomy 12 cases). Trisomy 12 and isolated RB1 deletion were seen in 14/120 cases, trisomy 12 and D13S319/D13S25 deletion with diploid RB1 in 19/118, and trisomy 12 and deletion encompassing the three 13q markers studied in 22/118 cases. The heterogenous distribution of trisomy 12 and 13q deletions within the neoplastic B cells suggests that they are secondary rather than primary events in CLL leukaemogenesis.

Trisomy 12 is seen within a specific subtype of B-cell chronic lymphoproliferative disease affecting the peripheral blood/bone marrow and co-segregates with elevated expression of CD11a

In order to delineate the specific morphological and immunophenotypic features of B-cell lymphoproliferative disorders associated with trisomy 12, 172 sequential unselected cases of CD19+CD5+ B-cell disorders, primarily affecting the peripheral blood and bone marrow, were studied. Trisomy 12 was found in 24 cases (13.9%), with all cases morphologically classified as either CLL-PL or CLL-mixed by FAB criteria. Trisomy 12 was not found in any cases of typical CLL. Trisomy 12 cases demonstrated a significant higher expression of CD11a (P<0.0001) and CD20 (P<0.0006) when compared to cases with the equivalent morphology and immunophenotype, but without the chromosomal abnormality. Trisomy 12 cases also demonstrated a higher frequency of FMC7, CD38 expression and moderate to strong surface immunoglobulin staining. However, no correlation was detected between the percentages of trisomy 12 cells and cells expressing CD11a, CD38, FMC7 or sIg mean fluorescent intensity. Cells from trisomy 12 positive cases were sorted according to their CD11a expression using fluorescent activated cell sorting. There was a significant increase in the percentage of trisomy 12 cells within the CD11a+ sorted fraction compared to the unsorted population (P < 0.05), implying that trisomy 12 is associated with increased expression of CD11a. With the highly specific morphological and immunophenotypic features demonstrated by trisomy 12 cases in this study, it is highly likely that these cases constitute a specific group of B-cell lymphoproliferative disorders.

Detection of trisomy 12 and centromeric alterations in CLL by interphase- and metaphase-FISH

We have studied trisomy 12 in chronic lymphocytic leukemia (CLL) by fluorescence in situ hybridization (FISH) with an alpha-satellite centromeric probe for chromosome 12 on both dividing and non-dividing cells. Trisomy for chromosome 12 was demonstrated in four of these patients (15.3%) using FISH on interphase cells. The percentage of trisomic cells ranged from 10% to 65% of nuclei. The hybridization signals in the trisomic and disomic nuclei were of a broadly similar size and nature. Interestingly, three of the remaining CLL patients, who exhibited disomy for chromosome 12, showed a marked difference in size of the hybridization signals in interphase nuclei. This was also demonstrated in metaphase spreads. In addition, metaphase FISH studies revealed a supernumerary marker chromosome in three out of 26 patients with CLL.

In B-cell chronic lymphocytic leukaemia chromosome 17 abnormalities and not trisomy 12 are the single most important cytogenetic abnormalities for the prognosis: a cytogenetic and immunophenotypic study of 480 unselected newly diagnosed patients

Of 560 consecutive, newly diagnosed untreated patients with B CLL submitted for chromosome study, G-banded karyotypes could be obtained in 480 cases (86%). Of these, 345 (72%) had normal karyotypes and 135 (28%) had clonal chromosome abnormalities: trisomy 12 (+12) was found in 40 cases, 20 as +12 alone (+12single), 20 as +12 with additional abnormalities (+12complex). Other frequent findings included abnormalities of 14q, chromosome 17, 13q and 6q. The immunophenotype was typical for CLL in 358 patients (CD5+, Slg(weak), mainly FMC7-) and atypical for CLL in 122 patients (25%) (CD5-, or Slg(strong) or FMC7+). Chromosome abnormalities were found significantly more often in patients with atypical (48%) than in patients with typical CLL phenotype (22%) (P < 0.00005). Also +12complex, 14q+, del6q, and abnormalities of chromosome 17 were significantly more frequent in patients with atypical CLL phenotype, whereas +12single was found equally often in patients with typical and atypical CLL phenotype. The cytomorphology of most of the +12 patients was that of classical CLL irrespective of phenotype. In univariate survival analysis the following cytogenetic findings were significantly correlated to a poor prognosis: chromosome 17 abnormalities, 14q+, an abnormal karyotype, +12complex, more than one cytogenetic event, and the relative number of abnormal mitoses. In multivariate survival analysis chromosome 17 abnormalities were the only cytogenetic findings with independent prognostic value irrespective of immunophenotype. We conclude that in patients with typical CLL immunophenotype, chromosome abnormalities are somewhat less frequent at the time of diagnosis than hitherto believed. +12single is compatible with classical CLL, and has no prognostic influence whereas chromosome 17 abnormalities signify a poor prognosis. In patients with an atypical CLL immunophenotype, chromosome abnormalities including +12complex, 14q+, del 6q and chromosome 17 are found in about 50% of the patients, and in particular chromosome 17 abnormalities suggest a poor prognosis.

Chronic lymphocytic leukaemia: the nature of the leukaemic cell

Far from being the boring, inactive, inert lymphocyte that haematologists of old perceived it to be, the chronic lymphocytic leukaemia (CLL) cell has set us many complex problems. The cell is apparently stuck in G0 in cell cycle, yet expresses many activation markers. The cells apparently manufacture many cytokines and respond in vitro to even more, yet cells entering even G1 are few. The cell surface marker profile is unique. There is apparently no normal equivalent of the CLL cell. In part, this may be because the cell is malignant; malignant cells often express aberrant markers. Consistent chromosomal abnormalities are emerging but we have no idea how these abnormalities translate into molecular mistakes that dictate the peculiar nature of the cell. CLL cells carry a characteristics set of adhesion molecules, but we cannot read their homing and recycling instructions. The outstanding irregularities of the CLL cell are its CD5 positivity and its sparse surface immunoglobulin. This ought to translate as an anergic B1 cell, perhaps programmed for autoimmunity. If the tumour cell were responsible for the patient's production of immunoglobulin or secretion of autoantibodies, then a pattern might have emerged. Alas, these are the product of the normal B cells. How the CLL cell induces these complications is unknown. Thus, despite the information contained in this review, the CLL cell remains a puzzle.

Differential Rates of Somatic Hypermutation in VH Genes Among Subsets of Chronic Lymphocytic Leukemia Defined by Chromosomal Abnormalities

Chronic lymphocytic leukemia (CLL) is a B-cell tumor involving small lymphocytes that generally express the CD5 antigen and low levels of surface Ig. Within this definition, there is heterogeneity among cases in cell morphology, karyotypic abnormalities, and clinical course. Trisomy 12, the most frequent karyotypic abnormality, is commonly found in a subset of CLL with atypical morphology. It has also been associated with advanced disease, and possibly with a less favorable prognosis. A further subset of cases with abnormalities involving chromosome 13q14 have typical lymphocyte morphology. Occasionally, the two abnormalities are found together. To assess the clonal history of the cell of origin in disease subsets defined by these two chromosomal abnormalities, we investigated the usage of VH genes and the pattern of somatic mutation in 10 cases of trisomy 12 with atypical morphology and eight cases of 13q14 abnormality with typical morphology. In addition, four cases with both chromosomal abnormalities were analyzed. Results confirm a common usage of the VH1 family in all subsets. However, the patterns of somatic mutation were distinct, with cases of trisomy 12 showing a minimal level of mutation (mean ± SD, 0.34% ± 0.86%) and cases of 13q14 abnormality showing significant levels (6.5% ± 1.67%). The four cases with both abnormalities showed a mixed pattern. All mutated cases had intraclonal homogeneity, and three of 10 had a pattern indicative of antigen selection. These results suggest that the clonal history of the two subsets of CLL may differ.

Biclonal B-cell chronic lymphocytic leukemia with inv(14)(q11q32)

Cytogenetic biclonality is a rare occurrence in chronic lymphocytic leukemia. A 59-year-old man was diagnosed to have B-cell chronic lymphocytic leukemia with typical morphology and immunophenotype (CD5+, CD19+, and CD23+). However, karyotypic analysis of the small lymphocytes showed the presence of two distinct unrelated clones, including one with inv(14).

Interphase cytogenetics in chronic lymphocytic leukemia

The incidence of trisomy 12 and 13q12-q14 abnormalities in patients with chronic lymphocytic leukemia (CLL) was determined by conventional cytogenetics and interphase fluorescence in situ hybridization (FISH). In the analysis of 580 consecutive patients, trisomy 12 was detected by conventional cytogenetics in 39 cases (9%) and 117 cases (20%) by FISH. Trisomy 12 was shown to be associated with advanced clinical stage, atypical morphology, and higher proliferative activity. Combined immunophenotyping and FISH showed that trisomy 12 was present only in a proportion of the clonal B-cells. These data suggest that trisomy 12 is a secondary event associated with features of disease progression. Sequential FISH showed clonal progression of the trisomic clone over time. Three hundred patients also were investigated for 13q deletions using FISH analysis of the RB1 locus (13q14). Monoallelic RB1 deletion was seen in 104 (34%) of cases. One case had a homozygous deletion in 90% of the cells. Dual-color FISH detected the presence of trisomy 12 and RB1 in 17 (5%) cases. DNA probes for 13q12.3 (BRCA2) and 13q14 (RB1 and DBM locus) were used in 35 cases. Twenty-eight (80%) cases showed deletion of a 1Mb 13q12.3 encompassing the BRCA2 locus, whereas 22/35 (63%) were deleted at 13q14. Our data suggest that abnormalities of 13q are more frequent than trisomy 12 in CLL and provide evidence for the presence of a new candidate gene at 13q12.3 that may be involved in the pathogenesis of CLL.

Genetic abnormalities in chronic lymphocytic leukemia and their clinical and prognostic implications

Clonal chromosome abnormalities can be detected in approximately 50% of patients with chronic lymphocytic leukemia (CLL). The most common changes are trisomy 12, followed by structural abnormalities of 13q, 11q, 6q, and 14q. By fluorescence in situ hybridization (FISH), these aberrations can be demonstrated even in cases with insufficient mitotic yield or a normal karyotype. The biologic consequences of trisomy 12 are unknown, but a gene dosage effect is suspected and studies on partial trisomy 12 indicate that the region 12q13 to 12q22 might be of particular pathogenetic importance. Trisomy 12 is strongly associated with atypical lymphocyte morphology and seems to be a secondary event in leukemogenesis, as shown by combined immunophenotyping and interphase FISH. Structural abnormalities of 13q frequently involve hetero- and homozygous deletions of a region in 13q14, distal to the retinoblastoma gene, which may be the site of a tumor suppressor gene. In contrast to a normal karyotype or structural changes of 13q, complex karyotypic abnormalities, high percentage of abnormal metaphases, trisomy 12 and structural changes involving the P53 tumor suppressor gene on 17p13 are adverse prognostic indicators. Cytogenetic and molecular findings provide important diagnostic, clinical, and prognostic information which can contribute to treatment decisions and follow-up of CLL patients.

Genes and chromosomes in chronic B-cell leukemia

Cytogenetic analysis of patients with chronic B-cell leukemia (B-CLL) indicates that 50% have chromosome abnormalities, while fluorescence in situ hybridization (FISH) and molecular techniques reveal an even higher incidence. Trisomy 12 and deletions or translocation of chromosome 13q14 are the most common abnormalities, but in neither case has the gene or genes involved in the abnormalities been identified. Combined FISH and immunophenotyping studies suggest that both abnormalities are secondary events in B-CLL. Other recurring chromosome abnormalities include 6q-, 11q- and 12p-, but the genes involved in these abnormalities have not been identified. Involvement of the BCL1, BCL2, and BCL3 genes has been reported, but the numbers are low and the cases tend to be atypical. Trisomy 12 in association with complex karyotypic abnormalities is associated with a poor prognosis, and FISH studies show a strong correlation between trisomy 12, atypical morphology, and advanced disease. Ten to 15% of patients have mutations of p53 which is associated with advanced disease, resistance to treatment, and poor survival.