Monoclonal Gammopathies |
1 Leukaemia Research Fund UK Myeloma Forum Cytogenetics Group, Human Genetics Division, University of Southampton, Wessex Regional Genetics Laboratory, Salisbury District Hospital, Salisbury, Wilts
2 Department of Haematology, Southampton University Hospital NHS Trust, Southampton General Hospital, Southampton
3 Cancer Sciences Division, University of Southampton, Southampton
4 Leukaemia Research Cytogenetics Group, Northern Institute for Cancer Research, Newcastle University, Newcastle-upon-Tyne, UK
Correspondence: Laura Chiecchio, Myeloma Cytogenetics Group, Wessex Regional Genetics Laboratory, Salisbury District Hospital, Salisbury, Wilts SP2 8BJ, UK. E-mail: laura.chiecchio{at}salisbury.nhs.uk
|
|
|---|
Design and Methods: Chromosome 13 deletion (
13), deletion of TP53, ploidy status and immunoglobulin heavy chain (IgH) translocations were evaluated by fluorescence in situ hybridization in patients with monoclonal gammopathy of undetermined significance (n=189), smoldering multiple myeloma (n=127) and multiple myeloma (n=400).
Results: Overall,
13 (25%, 34% and 47%), 16q23 deletions (6%, 8% and 21%) and 17p13 deletions (3%, 1% and 10%) were less frequent in patients with monoclonal gammopathy of undetermined significance and smoldering multiple myeloma than in those with multiple myeloma. When distinct genetic groups were considered, no differences in the prevalence of
13 were found with t(4;14)(p16;q32) and t(14;16)(q32;q23) among the three diagnostic groups; in contrast
13 was rarer in t(11;14)(q13;q32) in patients with monoclonal gammopathy (1/28) and smoldering myeloma (2/13) than in those with multiple myeloma (40%). Similar results were seen for the few t(6;14)(p21;q32) cases: 0/3 patients with monoclonal gammopathy or smoldering myeloma had the
13, whereas 4/6 (67%) patients with multiple myeloma and this translocation also had the deletion. In multiple myeloma patients with both an IgH translocation and
13, the proportions of cells affected by the two abnormalities were similar, as was the case for t(4;14) and t(14;16) monoclonal gammopathy patients positive for
13. In contrast, in monoclonal gammopathy patients with t(14;20)(q32;q11), the translocation was present in almost all cells, while the
13 was present in only a sub-population.
Conclusions: These results indicate that the presence and time of occurrence of
13 depends on the presence of specific concurrent abnormalities. The observation that
13 was extremely rare in monoclonal gammopathy of undetermined significance and smoldering multiple myeloma with translocations directly involving cyclin D genes (CCND1 and CCND3) suggest a possible role of
13 in the progression of the disease specifically in these genetic sub-groups. (clinicaltrials.gov identifier: ISRCTN 68454111; UKCRN ID 1176).
Key words: deletion 13, plasma cell dyscrasias, genetic context.
|
|
|---|
The paucity of plasma cells within the bone marrow of patients with MGUS, together with the low proliferative capacity of these cells, has precluded significant karyotypic studies in these patients. Interphase fluorescence in situ hybridization (FISH) provides an alternative approach to investigate chromosomal aberrations in tumor cells from which metaphases are difficult to obtain. Using interphase FISH, chromosomal aberrations were consistently detected in a high proportion of MGUS patients, with roughly 50% of them carrying one of the primary IgH translocations and the remaining patients displaying a hyperdiploid karyotype. These findings suggested that ploidy status and IgH rearrangements were early events delineating different pathogenic pathways.6–9
Conflicting results have been reported on the prevalence of deletion/monosomy 13 (
13) in MGUS. Avet-Loiseau et al. found a substantially lower frequency of this abnormality in MGUS (~25%) than in MM (~50%),10,11 while others reported a similar incidence in both conditions.7,12 Fonseca et al. also indicated that when
13 was detected in MGUS it occurred in the majority of clonal plasma cells,7 consistent with that normally observed in MM,13,14 while others reported a greater heterogeneity in MGUS.13 There has also been controversy regarding the prognostic significance of
13 in MM. This chromosomal aberration, detected by interphase FISH, was one of the first established genetic prognostic factors, independent of the mode of treatment.15 However, it now appears that the dismal prognosis previously thought to be conferred by the deletion is actually due to its association with other poor-risk genetic markers, such as specific primary IgH translocations or TP53 deletions,16,17 and that
13 on its own probably does not affect prognosis.
In this study, we used interphase FISH to assess the incidence and the association of
13 with IgH translocations, ploidy status and deletions of 16q23 and TP53 in a large series of MGUS and SMM patients. We compared the results with the frequencies found in a group of newly diagnosed MM patients in order to determine whether the patterns of chromosomal aberrations differ within the different diagnostic groups. We also explored the clonal heterogeneity of MGUS by comparing the frequencies of the different chromosomal aberrations detected in individual patients.10
|
|
|---|
Cytogenetic testing
Density gradient centrifugation of bone marrow aspirates over Lymphoprep was performed to separate mononuclear cells by standard protocols. CD138+ plasma cells were isolated by magnetic-activated cell sorting using anti-CD138 immunobeads (Miltenyi Biotec Ltd., Bisley, UK). Interphase FISH was performed on plasma cells using a panel of commercial and in-house probes, as previously described.19,20 Results were available for
13, IgH rearrangements, t(4;14)(p16;q32), CCND3 break-apart (6p21), t(11;14)(q13;q32), t(14;16)(q32;q23), MAFB break-apart (20q11), deletion of TP53 (17p13) together with 17 centromere, and ploidy status. The interphase FISH method used to estimate ploidy and classify patients into groups with and without hyperdiploidy had been previously designed and assessed in MM patients,20 using a modification of the method described by Wuilleme et al.21 Break-apart patterns for the CCND3 or the MAFB probes in cases with a concomitant break-apart of the IgH probe were suggestive of t(6;14) and t(14;20), respectively. Cases with a suspected t(14;20) were tested using a fusion probe approach to confirm the presence of the translocation.
The cut-off levels for interphase FISH scoring recommended by the European Myeloma Network (EMN) FISH workshop (10% for fusion/break-apart probes and 20% for numerical abnormalities) were followed.
Statistical analysis
The frequencies of chromosomal aberrations in the groups of patients were compared by Fishers exact test or the Kruskall-Wallis test, as appropriate.
|
|
|---|
Table 1 summarizes the frequencies of the specific chromosomal aberrations within each diagnostic group. The incidence of
13 was substantially lower in MGUS (25%) and SMM (34%) than in MM (47%); the difference across the three groups was statistically highly significant (Kruskall-Wallis test: MGUS versus SMM versus MM, p<0.001).
|
View this table: [in a new window] [Download PPT slide] |
Table 1. Incidence of specific chromosomal abnormalities in the three groups of patients with MGUS, SMM and MM.
|
Patients with MGUS and SMM were classified as being hyperdiploid or not in the same way as previously described for MM.20 The distribution into the two ploidy classes differed between the diagnostic groups. A hyperdiploid karyotype was indicated in 63% of SMM and 57% of MM patients, while only 42% of MGUS cases were assigned to this category. The non-hyperdiploid MGUS group also included those patients found to be negative for all the interphase FISH tests performed; in MGUS these patients represented 11% of the total group and accounted for most of the difference between the groups.
IgH rearrangements involving the five recurrent loci (4p16, 6p21, 11q13, 16q23 and 20q11) were highly associated with a non-hyperdiploid karyotype in all three diagnostic groups: 94% of MGUS cases, 82% of SMM cases and 73% of MM cases with one of these IgH translocations were found in the context of non-hyperdiploidy (p<0.001 for all diagnostic groups). In contrast 35 of 49 MM cases with an IgH rearrangement not involving one of these loci were found in association with hyperdiploidy (p=0.043). In the SMM group the six unidentified IgH rearrangements were equally distributed between the two ploidy groups. In MGUS, 12 of 16 unidentified IgH rearrangements were found in the context of a non-hyperdiploid karyotype but the association was not statistically significant (p=0.18).
Percentage of plasma cells in patients with chromosome 13 deletion
When present,
13 involved a variable proportion of plasma cells (Figure 1). The median percentage of plasma cells carrying the abnormality was 65% in MGUS, 88.5% in SMM and 95% in MM. No variation was seen for illegitimate IgH rearrangements: in patients with MGUS the median percentage of cells displaying a 14q32 translocation was 91.5% (range, 24%–100%). The level of plasma cell involvement by different chromosomal aberrations was compared for all MGUS patients who exhibited
13 with at least one other abnormality (Table 2). Because of the differences in false positive rates between probes, unequivocal evidence of heterogeneity within the neoplastic clone was only accepted when the difference in the proportions of cells affected by distinct chromosomal aberrations was 30% or more. In 16 of 47 patients with
13, the abnormality was present in 60% or less of plasma cells (cases 1–16 in Table 2); of these 16 cases, 12 had other chromosomal aberrations for comparison. In all but three of these 12, the plasma cell involvement by the non-
13 abnormality was at least 30% greater than that shown by
13.
![]() View larger version (15K): [in a new window] [Download PPT slide] |
Figure 1. Distribution of the percentages of abnormal plasma cells with 13 in patients found positive for the abnormality, among the three groups of patients.
|
|
View this table: [in a new window] [Download PPT slide] |
Table 2. List of 47 MGUS patients with 13 ordered on the basis of the percentage of plasma cell involvement by the abnormality. For each case, concomitant numerical or structural abnormalities are specified with the percentage of plasma cell involvement (UIP, unidentified partner).
|
13 showed the same proportion (±5%) of plasma cells with the two abnormalities. In contrast, four of five (80%) cases of t(14;20) MGUS with
13 showed at least 30% fewer
13-positive plasma cells (median 51%) than t(14;20)-positive ones (median 95%). In MM, seven of nine (78%) cases of t(14;20) were associated with
13 and the median difference in plasma cell involvement by
13 and the translocation was 10% (range, 0–27%). In MGUS, 16q23 deletions were often present in a sub-clone of plasma cells (median, 63%; range, 23–100%), while in MM the median percentage of plasma cells with the abnormality was 87% (range, 21–100%). Those MGUS cases in which the proportion of plasma cells carrying the 16q deletion was small displayed at least one of the other chromosomal aberrations in the majority of clonal plasma cells (deletion 16q23 versus other chromosomal aberrations: 23% versus 82% IgH split; 33% versus 93% deletion 14q32; 44% versus 92% IgH split; 47% versus 99% IgH split).
Association of chromosome 13 deletion with other abnormalities
Table 3 shows the association between
13 and other chromosomal aberrations. The
13 was less frequently associated with any of the IgH rearrangements in MGUS than in MM (MGUS versus MM, 34% versus 60%; p<0.001). However, when the individual translocations were examined, no differences were found in the frequencies of association of t(4;14), t(14;16), or t(14;20) with
13 among the three diagnostic groups.
|
View this table: [in a new window] [Download PPT slide] |
Table 3. Association between 13 and the different chromosomal abnormalties.
|
13 was found in 40% of t(11;14) cases and involved a large proportion of plasma cells (>85%) while only one of 28 (3.6%) MGUS cases with t(11;14) had
13 (p<0.001). Furthermore, in this case, only 45% of the plasma cells had
13, while the translocation was present in all cells. In SMM only two of t(11;14) cases had
13 (15%), but this was not significantly different from the percentage found in MM. Both SMM patients had
13 in 70% of their plasma cells and the translocation in 100%. In this study, the presence of t(6;14) was detected in only 1–2% of patients, in agreement with other reported series. Despite the small number of cases, it was notable that
13 was present in four of the six (67%) MM cases, while in MGUS the two t(6;14) were both negative for
13 (in one of these two cases, 12% of the plasma cells carried the deletion).
|
|
|---|
13 in the pre-malignant conditions than in MM. This is in accordance with findings reported by Avet-Loiseau et al.10 The frequency of
13 progressively increased from MGUS to SMM to MM, suggesting a possible role of this abnormality in disease progression. The incidence of deletion of 16q23 and TP53 also increased progressively from MGUS to MM (p<0.001 and p=0.003, respectively). In contrast, a similar frequency of IgH rearrangements was observed in the three groups. When the individual incidences of the specific translocations were compared, only t(4;14) was significantly less frequent in MGUS, in agreement with other reports.7,10
Interphase FISH was used to classify patients according to their ploidy status into those with hyperdiploidy and those without.
13 was found more frequently in patients with a non-hyperdiploid karyotype than in those with hyperdiploidy in all three groups of patients (MGUS, 15% versus 32%; SMM, 21% versus 52%; MM, 34% versus 66%), suggesting that the specific association between
13 and non-hyperdiploidy, extensively reported in MM,15,17 is already established at the stage of MGUS. These findings differ from those reported by Brousseau et al.22 In MGUS, they found
13 more frequently in patients with hyperdiploidy (11/29, 38%) than in those without (3/27, 11%), although the reverse association was seen in MM. They defined ploidy by measuring the plasma cell DNA content using the Feulgen reaction and image cytometry. We are unable to explain this discrepancy although the fact that ploidy was evaluated by two different methods may be partially responsible. Pseudodiploidy and low chromosome count hyperdiploidy (48–49 chromosomes) are potentially difficult to identify by interphase FISH, compared to true hypodiploidy or high chromosome count hyperdiploidy. However, the comparison of our interphase FISH ploidy results with actual karyotypes for those MGUS (n=8) and SMM (n=24) patients with abnormal cytogenetics showed that all cases but one were accurately classified. Thus interphase FISH misclassification of ploidy is unlikely to account for the significant difference in results between the two series.
Abnormalities of 14q32 were observed in the majority of clonal plasma cells, independently of the stage of the disease, whereas the percentages of plasma cells carrying
13 or the 16q23 deletion varied significantly between MGUS, SMM and MM, with MGUS patients showing the greatest heterogeneity. In MGUS,
13 was often present in a sub-clone of the abnormal plasma cells. Although low level clones in MGUS may be due to only a small proportion of the CD138-positive plasma cells being part of the neoplastic clone, our results indicate that, in these cases, the
13 is a later change following IgH translocations or multiple trisomies. Similar findings were observed for most low level 16q23 deletions in which the cells were found to be 100% positive for other chromosomal aberrations.
Our results clearly show that the time of occurrence of specific abnormalities is crucially dependent on genetic context. The t(4;14), t(14;16) and t(14;20) are highly associated with
13 in MM.15,17,20 The same association was observed in MGUS and SMM patients. Moreover, in cases with t(4;14) and t(14;16), IgH rearrangement and
13 were found in a similar proportion of abnormal cells in the three diagnostic groups, suggesting that
13 occurred early in disease pathogenesis. However, a different time of occurrence of
13 was observed in relation to t(14;20). In MGUS,
13 appeared to originate later than t(14;20). A striking difference between MGUS and MM was seen regarding the association of
13 with t(11;14). While in MM 21/53 of t(11;14) cases also showed
13, in MGUS only 1/28 of cases with the translocation was associated with
13 (p<0.001). In MM the median percentage of plasma cells carrying the
13 in patients with t(11;14) was 98% while in the only case of MGUS with both t(11;14) and
13, all the plasma cells were positive for t(11;14) but only 48% of the plasma cells had
13. The translocation t(11;14) has been related to t(6;14) on the basis of a similar biological and clinical behavior.23 Both translocations directly activate a cyclin D family member (CCND1 and CCND3, respectively) and gene expression profiling studies demonstrated that cases carrying either one or the other translocation exhibited dysregulation of similar transcriptional programs showing overlapping gene expression profiles.23,24 As for t(11;14),
13 was not found in the MGUS cases with t(6;14), while it was present in the majority of MM cases with this translocation.
These findings are consistent with those reported by Bochtler et al.,25 who applied an oncogenic tree model to study patients with amyloid light chain amyloidosis, MGUS and MM, in order to detect clustering of chromosomal abnormalities. Patients with amyloidosis and MGUS showed the t(11;14) branch independent of
13, while t(4;14), and gain of 1q21 were grouped together with
13. In our study,
13 occurred less frequently in SMM cases with t(11;14), but not to a degree that was statistically significantly different from the MM group.
Conclusions
In this study, we examined a range of numerical and structural chromosomal changes in MGUS, SMM and MM patients. None of the chromosomal aberrations tested was exclusive to a single diagnostic group, confirming the extensive overlap between the different conditions from a genetic point of view. However, statistically significant differences were observed in the incidence of specific abnormalities between the three conditions, in particular for
13, 16q23 deletion and TP53 deletion. In MGUS, the greatest variation in the proportion of abnormal plasma cells carrying the abnormality was seen for
13 and 16q23 deletion. In particular, the temporal appearance of
13 was related to the presence of specific concomitant abnormalities: early when t(4;14) or t(14;16) was present, later with t(14;20), and even later with t(11;14) or t(6;14). These data suggest a possible role of
13 in the transition from MGUS to MM specifically in cases with t(11;14) or t(6;14).
LC designed and performed research, analyzed data and wrote the first draft of the paper; GPD, AHI, EDC, RKMP and DMS performed research; KHO, NCPC and CJH contributed to the analysis of the data; FMR designed and performed research, and analyzed data. All the authors contributed to the final draft of the paper. The authors reported no potential conflicts of interest.
Received for publication May 8, 2009. Revision received June 11, 2009. Accepted for publication June 29, 2009.
|
|
|---|
| ||||||||||||||||||||||||||||||||||||||||||||||