Clinical impact of chromosomal aberrations in multiple myeloma

Authors


Gösta Gahrton, Department of Medicine, M54 Karolinska University, Hospital Huddinge, 141 86 Stockholm, Sweden.
(fax: 46-8-7748725; e-mail: Gosta.Gahrton@ki.se).

Abstract

Abstract.  Nahi H., Sutlu T., Jansson M., Alici E., Gahrton G. (Karolinska Institutet, Karolinska University Hospital Huddinge; Hematology Centre, Karolinska University Hospital, Huddinge, Stockholm, Sweden) Clinical impact of chromosomal aberrations in multiple myeloma (Review). J Intern Med 2011; 269: 137–147.

Chromosomal aberrations are frequently found in multiple myeloma cells and play a major role in patient outcome and management of the disease. The most important chromosomal aberrations associated with poor outcome are del(17p), t(4;14), t(14;16) and t(14;20). Others that may be associated with adverse prognosis include amp(1)(q21), del(1p32), del(13), del(8p21) and hypodiploidy. Many chromosomal aberrations have no or uncertain impact; for example, t(11;14), t(8;14) and hyperdiploidy. Attempts have been made to overcome the negative prognostic impact of chromosomal aberrations using autologous or allogeneic transplantation or new immunomodulatory drugs such as thalidomide, lenalidomide and the proteasome inhibitor bortezomib, but the results are controversial. Data suggest that allogeneic transplantation and treatment with bortezomib or lenalidomide may help to overcome the negative effect of del(13) on prognosis, whereas bortezomib may have some influence on reducing the impact of del(17p), t(4;14) and t(14;16). Chromosome analysis should always be performed at diagnosis of multiple myeloma to improve the prediction of outcome and to aid treatment decision-making.

Introduction

Multiple myeloma (MM) is a heterogeneous disease with different outcomes; the overall survival (OS) ranges from a few months to decades in some cases [1, 2]. Identification of chromosomal abnormalities is currently one of the most important tools for predicting outcome. Chromosomal aberrations associated with MM were first described in the late 1970s [3] and early 1980s [4]. In 1985, their prognostic importance was demonstrated by Dewald et al. [1] in a study based on conventional cytogenetic methods. They found that the main chromosomal abnormalities involved chromosomes 1, 11 and 14. With the advent of new techniques such as fluorescence in situ hybridization (FISH) and multi-target FISH (M-FISH), the number of chromosomal aberrations identified has increased and so has the number of aberrations with prognostic importance.

Increasing evidence has shown the importance of aberrations involving the immunoglobulin heavy chain (IgH) locus at 14q32. This region has strong transcriptional activity in B cells, and the translocation of an oncogene close to this locus may result in dysregulation of its expression [5]. As suspected, many B cell tumours, including MM, have chromosomal translocations mediated by recombination errors, which position an oncogene under the influence of a strong immunoglobulin enhancer. Chromosomal aberrations involving 14q32 include t(4;14), t(11;14), t(14;16) and t(14;20). Several other chromosomal abnormalities have been studied in MM, such as 1q gains, 1p deletions, del(13q) and del(17p) [6]. Many of the chromosomal aberrations observed in MM are also seen in monoclonal gammopathy of undetermined significance (MGUS), corroborating evidence from recent studies indicating that MM is almost always preceded by MGUS [7].

There are many other well-established factors that predict outcome in MM, for example β2-microglobulin (β2M), creatinine and haemoglobin (Hb) levels. The International Staging System (ISS) for MM relies on β2M as one of the most important tumour burden markers correlating to the aggressiveness of the disease. It is highly significant in almost all multivariate analyses as an independent prognostic factor. Although chromosomal aberrations have not yet been included in the current staging systems, growing evidence suggests that detailed chromosome analysis will surpass the ISS for prognostic information. Clearly, further studies are needed to provide information for designing a new system.

Specific chromosomal aberrations

1q gains and 1p deletions

Structural aberrations of chromosome 1 are the most frequent chromosomal aberrations in MM and are identified in 40–48% of all cases [1, 8]. The most common aberration is amp(1)(q21), which is seen in 40% of all newly diagnosed cases of MM and in about 70% of cases of relapse [9], although it is relatively rare in MGUS. Gains of 1q are frequently seen at late stages of MM; thus, the locus is considered to play a pathogenetic role in disease progression and gains are therefore associated with poor prognosis [9–11]. Elevated expression of the cell cycle-related gene CKS1B that is located in this region strongly correlates with amp(1)(q21) and is a predictor of poor survival [12–14]. It has been suggested that CKS1B increases tumour aggressiveness by regulating the ubiquitination and subsequent breakdown of the cyclin-dependent kinase inhibitor p27Kip1, thereby favouring cell proliferation [15, 16].

Deletion of 1p is estimated to occur in 7–40% of patients with MM [17–19]. The region 1p32 is deleted in 15% of patients with MM, leading to decreased expression of the CDKN2C gene. CDKN2C is a cyclin-dependent kinase inhibitor targeting mainly CDK4 and CDK6 and functions as a cell growth regulator that controls cell cycle G1 progression. The deletion and subsequent downregulation of CDKN2C expression is believed to trigger progression of MGUS to MM, and patients with this aberration are considered to have a worse OS than those who do not carry the deletion [20]. Another commonly deleted region on this chromosome is 1p12; however, this region does not seem to affect prognosis in MM [20] (Table 1).

Table 1. Common chromosomal aberrations in multiple myeloma, occurrence and median overall survival after intensive treatment
AberrationIncidence found by FISH (%)Patients with aberration/total examinedMedian OS post-HDT (months): patients with aberrations vs. all otherMedian follow-up time (months)References
  1. HDT, high-dose therapy; NR, not reached.

  2. aMinimum follow-up time.

  3. bNot examined by FISH.

  4. cCompared with normal karyotype.

1q gain30–3746/15930 vs. 3855Fonseca, et al. [97]
1p loss1836/20339 vs. 8236Chang, et al. [98]
t(4;14)13–2022/16832 vs. NR27Moreau, et al. [36]
  68/669Avet-Loiseau, et al. [99]
  26/15319 vs. 4436aGertz, et al. [37]
t(11;14)15–1726/168NR vs. NR27Moreau, et al. [36]
  105/669Avet-Loiseau, et al. [99]
  34/19736 vs. 3436aGertz, et al. [37]
t(14;16)2–1015/32316 vs. 4141Avet-Loiseau, et al. [23]
  14/669Avet-Loiseau, et al. [99]
8p loss2414/4424 vs. 6758Sutlu, et al. [44]
Hypoploidy9b131/984b19 vs. 51c48Fassas, et al. [54]
Hyperploidy39256/657NR vs. NR41Avet-Loiseau, et al. [6]
del(13q)5042/11027 vs. 6548Facon, et al. [100]
  449/936NR vs. NR41Avet-Loiseau, et al. [23]
del(17p)10–1110/10515 vs. 4820Chang, et al. [60]
  58/53222 vs. NR41Avet-Loiseau, et al. [6]
  18/16815 vs. 3936aGertz, et al. [37]

IgH aberrations

Translocations at 14q32, a region that encodes the IgH locus, are common aberrations in MM, resulting from illegitimate IgH rearrangements [21]. IgH translocations are probably early events in MM tumorigenesis because they seem to have the same prevalence in MGUS. Translocations involving the IgH gene are detected in more than 50% of patients with newly diagnosed MM and are associated with a nonhyperdiploid karyotype [22]. The most common IgH translocations are t(4;14)(p16.3;q32) and t(11;14)(q13;q32); together their prevalence is 30–40% in patients with MM. The translocation t(14;16)(q32;q23) occurs in about 5% of patients. Less frequent translocations include t(6;14)(p21;q32), t(8;14)(q24;q32) and t(14;20)(q32;q11). Different IgH translocations can readily be identified in the same cell because the FISH panel can include different translocation probes such as t(4;14), t(11;14) and t(14;16) and at the same time a two-colour IgH probe with the V-region part in one colour and the C- and J-region parts in another. With this probe, it is possible to identify a split in the gene indicating fusion with another gene and deletions within the IgH gene simultaneously (Fig. 1).

Figure 1.

 FISH analysis. The cell on the left has a t(4;14) translocation: one red signal for FGFR3 (4p16) (upper left), two green signals for IgH (14q32) and two yellow fusions signals (lower left and right). The cell on the right is normal: two red and two green signals.

t(4;14), t(14;16) and t(14;20).  Almost all studies of the translocation between 14q32 and 4p16 (t(4;14)) have reported a negative impact, which is independent of the type of treatment and other prognostic factors. Translocation t(4;14) is identified by conventional cytogenetic analysis but t(14;16) may easily be overlooked by this technique. Patients with t(14;16) have an equally aggressive disease as those with t(4;14) [23]; however, because of the lower frequency of t(14;16), its significance has only been shown conclusive in larger studies [23]. At present, t(4;14) and t(14;16) translocations are considered to be specific for MM; no other known malignancy carries these aberrations.

The fibroblast growth factor receptor 3 gene (FGFR3) is an oncogene that is dysregulated by t(4;14)(p16.3;q32.3) [24]. FGFR3 is a receptor tyrosine kinase [25] and is thus a possible target for therapy with receptor tyrosine kinase inhibitors [26]. Another gene that is dysregulated by the t(4;14) is the multiple myeloma SET domain protein (MMSET) [27], which is also an oncogene that contributes to cellular adhesion and clonogenic growth [28]. Of all cases with t(4;14), MMSET is dysregulated in 100% and FGFR3 in about 70% [29]. t(14;16)(q32;q23) also causes overexpression of c-Maf (musculoaponeurotic fibrosarcoma) [30], which is a proto-oncogene [31]. Another Maf gene is MafB, the expression of which is highly correlated with t(14;20)(q32;q12), a translocation occurring in about 1–2% of all MM cases and strongly associated with poor prognosis [32–34]. Knowledge of the molecular causes of the clinical effect of chromosomal aberrations is of great value for future design of targeted therapy and may provide the means to overcome the negative prognostic impact of these aberrations.

t(11;14).  This aberration, found in about 15–17% of patients with MM, is exactly the same as the t(11;14)(q13;q32) of mantle cell lymphoma. The t(11;14) is associated with upregulation of cyclin D1 [35] and has been widely described as having either a favourable [36] or no impact [37] on OS (but not a negative effect). Compared to patients without this aberration, MM patients with t(11;14) are more likely to have a nonsecreting disease, morphology of a “lymphoplasmacytic” type and a higher frequency of immunoglobulin M disease [38, 39]. Cyclin D1, detected by immunohistochemical analysis, identifies MM patients with the t(11;14) [35].

t(6;14).  Translocation (6;14)(p21;q32) has a prevalence of approximately 4% in patients with MM [40]. This translocation is not restricted to MM, but is also detected in non-Hodgkin’s lymphoma [41]. No data on survival are available because of the low frequency of occurrence, but it is known that cyclin D3 is dysregulated as a result of t(6;14) [40].

8p21 and 8q24

8p21.  Previous studies have linked molecular dysregulations originating from changes in the 8p21 region to various malignancies including leukaemic mantle cell lymphoma [42] and B cell lymphoma [43], and the loss of this region has been shown to have a negative effect on survival in head and neck cancers. Our group has previously reported that del(8)(p21) is an independent predictor of poor prognosis in MM, and both progression-free survival (PFS) and OS are adversely affected [44]. A more recent study has presented a similar frequency of occurrence for del(8)(p21) and confirmed the negative effect on both PFS and OS. However, the statistical significance was lost after the p-values were adjusted for ISS criteria [44, 45].

Analysis of the genes located at this locus leads to promising therapeutic targets such as the tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor, bone morphogenetic protein (BMP)1, BMP2, BMP4, the pro-apoptotic mitochondrial protein Nix (BNIP3L) and the tumour suppressor gene SCARA3. It is possible that the downregulation of TRAIL receptor expression on the cell surface because of del(8)(p21) might reduce the sensitivity of tumour cells to TRAIL-mediated apoptosis [46], and help them to escape from immune surveillance by NK cells or CTL:s [47]. Nevertheless, further studies at the molecular level are needed to identify the mechanisms behind the effect of 8p21 deletion in MM.

8q24.  8q24 encodes the c-Myc gene. Gene expression profiling studies have demonstrated that the MYC pathway is a key player in the evolution of normal plasma cells to MM [48]. Translocations and breakpoints involving this locus have proven to be quite heterogeneous [49] and the most well known is t(8;14)(q24;q32), which is associated with Burkitt’s lymphoma and non-Hodgkin’s lymphoma and has also been described in MM. The same region could be involved in translocations with other chromosomes; c-Myc rearrangements are found in about 15% of MM patients with no clear relation to outcome [50].

Ploidy

Based on chromosomal analysis, the chromosome number pattern is a powerful prognostic factor in patients with MM. In general, loss of genetic material (hypodiploidy) in almost all malignancies is a marker of poor prognosis, whereas gains (hyperdiploidy) are usually associated with better outcome.

Hypoploidy.  The incidence of hypodiploidy is about 10% [51, 52]. The importance of hypodiploidy for OS in MM is unclear. An adverse effect of hypodiploidy in general may be because of monosomy of specific chromosomes, where the general hypodiploidy might be a confounding factor. However, correlations with adverse OS have been found in multivariate analysis independent of other cytogenetic aberrations [53, 54].

Hyperploidy.  Trisomies of chromosomes 3, 5, 7, 9, 11, 15 and 19 have been repeatedly reported to be involved in MM patients with hyperploidy (≥47 chromosomes) and are observed in 50–60% of cases [53, 55]. Hyperdiploidy seems to be stable during the course of the disease [56] and appears to be weakly associated with a favourable outcome [6, 56], provided that it does not occur together with unfavourable IGH translocations or 17p deletions. However, these combinations are unusual. Hyperdiploid cases with 5q31 gain were reported to have a better outcome than hyperdiploid cases without this characteristic, whereas there was no survival difference between the nonhyperdiploid and hyperdiploid cases without 5q31 gain [57]. This observation suggests that the favourable prognostic impact of hyperdiploid MM is because of gain of 5q34.

Chromosome 13

Deletion of 13q or the whole chromosome 13, identified by FISH in slightly less than 50% of patients with MM, has for many years been considered to be an adverse prognostic factor [58]. However, in earlier studies the association with poor prognosis was based on conventional cytogenetics, whereas in most newer studies, using FISH and multivariate analysis including other chromosomal abnormalities, the loss of 13q is not an independent prognostic factor [6, 37, 59–61]. Loss of 13q/-13 detected by karyotype analysis is still considered by some to be an indicator of extremely poor prognosis; however, other aberrations will remain undetected unless a comprehensive FISH analysis with several probes is performed alongside conventional karyotype analysis. Such analysis generally demonstrates that the negative impact on prognosis is not limited to del(13q)/-13, but is because of the association with t(4;14) and/or del(17p) [6].

Del(17p), TP53

The protein p53 has an important role in cell cycle control and tumour development. Normal cells usually show very low expression of p53, which has a short half-life because of rapid turnover mediated by ubiquitination and proteolysis [62]. DNA-damaging drugs rapidly induce a transient increase in p53 [63]. Once activated, p53 induces cell cycle arrest and apoptosis. Mutations of TP53 are considered to be associated with resistance to cytotoxic drugs [64]. Whereas mutated TP53 is common in many types of tumours, it is found in only about 10% of all newly diagnosed cases of MM, but with increasing frequency in late disease. This genetic aberration is a predictor of extremely low OS and the lowest rate of achieving complete remission in comparison with other abnormalities or none [57, 65]. Deletion of 17p is probably one of the most predictive molecular markers for resistance to therapy and short OS in MM identified so far [10, 65]. Neither high-dose therapy (HDT) nor allogeneic transplantation seems to overcome the extremely poor prognosis for patients with TP53 deletions/mutations [60, 65].

Prognostic impact related to treatment modality

Autologous stem cell transplantation

Autologous stem cell transplantation (ASCT) is still considered the gold standard for treatment of patients with MM younger than 65 years of age, mainly based on two prospective trials [66, 67]. There are many alternative pretreatment modalities (i.e., alternate induction and conditioning treatment before the actual infusion of the stem cells) [68]. Also, ASCT can be given as a single transplant or as two transplants in tandem [69]. Conditioning is performed using melphalan 200 mg m−2 in most studies of the impact of chromosomal aberrations, whereas induction modalities vary between studies.

Induction treatment with vincristin, adriamycin and dexamethasone (VAD) followed by HDT (melphalan 200 mg m−2) was until recently a standard regimen prior to autologous stem cell infusion. Chang et al. [59] published data on 128 patients with MM treated according to this regimen. Translocation t(11;14) was found in 13% and t(4;14) in 12%. No difference in PFS or OS was found between patients with or without t(11;14), and the treatment could not neutralize the negative impact of t(4;14) [59] or del(17p) [45, 60]. Single or tandem ASCT did not affect the outcome of patients with t(4;14) [36].

Two phase II studies using bortezomib and dexamethasone as induction treatments prior to ASCT showed no difference in response rate (RR) between patients with and without t(4;14) [70, 71]. However, the number of patients included was low, and no survival data are available. Barlogie et al. showed an improvement in RR and OS in patients both with and without cytogenetic abnormalities by incorporating bortezomib into a melphalan-based tandem transplant regimen and a maintenance treatment post-ASCT (total therapy 3) [72, 73]. In a large trial of the Intergroupe Francophone du Myelome (IFM) including 436 patients (of whom 15% had t(4;14) and 11% had del(17p)) treated with bortezomib plus dexamethasone followed by ASCT, the negative impact of t(4;14) could be neutralized, but not that of del(17p) [74].

The presence of del(13q) did not affect the relapse rate or OS. This lack of effect was observed after both single and tandem ASCT and regardless of whether VAD or a novel agent had been used for induction before HDT [6, 37, 45, 70, 75] (Table 2).

Table 2. Prospective comparative studies on impact of chromosome aberrations after high-dose treatment
 RegimenPFS (months or percentage of patients at the median follow-up)Median OS (months or %)Median follow-up time (months)References
  1. PFS, progression-free survival; OS, overall survival; VAD, vincristin, adriamycin and dexamethasone; MEL200, melphalan 200 mg m−2; MEL140, melphalan 140 mg m−2; Allo-RIC, reduced-intensity allogeneic transplantation.

  2. aNo statistical significance.

t(4;14)/no t(4;14)VAD/MEL2009.9 vs. 25.818.3 vs. 48.120Chang, et al. [59]
 VAD/MEL140/MEL20020.6 vs. 36.541.3 vs. NR41Moreau, et al. [36]
t(11;14)/no t(11;14)VAD/MEL20025.2 vs. 25.7a37.2 vs. 46.3a20Chang, et al. [59]
 VAD/MEL140/MEL20035 vs. 34aNR vs. NRa41Moreau, et al. [36]
del(17p)/no del(17p)VAD/MEL2007.9 vs. 25.714.7 vs. 48.120Chang, et al. [60]
 VAD/MEL140/MEL20015 vs. 3522 vs. NR41Avet-Loiseau, et al. [6]
t(4;14)/no t(4;14)Allo-RIC50% vs. 45%a39% vs. 49%a33Schilling, et al. [65]
t(11;14)/no t(11;14)Allo-RIC36% vs. 45%a36% vs. 49%a33Schilling, et al. [65]
del(17p)/no del(17p)Allo-RIC28% vs. 43%30% vs. 49%33Schilling, et al. [65]

Although ASCT – single or tandem – is still considered the gold standard treatment for MM, it may be challenged by the use of new drugs. Also, a recently performed meta-analysis including randomized trials (a total of 2411 patients) of single ASCT versus conventional chemotherapy showed that ASCT resulted in significantly longer PFS, but with no significant impact on OS [76]. It is therefore possible that the prognostic impact of chromosomal aberration may change with the introduction of new drugs, with or without previous or subsequent ASCT. New prospective trials are in progress comparing ASCT and new drug treatment without ASCT. The additional component of these studies to assess the impact of chromosomal aberrations may clarify their prognostic role with either treatment modality [77, 78].

Allogeneic stem cell transplantation

Allogeneic stem cell transplantation with myeloablative conditioning is a controversial treatment modality in MM. Although the relapse rate is lower than with ASCT, the treatment-related mortality (TRM) is as high as 30–50% [79, 80]. By using reduced-intensity conditioning (RIC) allogeneic transplantation, the TRM could be reduced to <20% [81, 82], and in prospective comparisons with ASCT to as little as 12% [83]. Although the relapse/progression rate was higher than with myeloablative conditioning, the PFS and OS compared favourably to single and tandem ASCT in two recent prospective studies in which a tandem ASCT-RIC approach was used [84, 85].

Data on the prognostic impact of cytogenetic aberrations after allogeneic transplantation are scarce. Schilling et al. [65] showed that RIC could not overcome the poor prognostic impact of del(17)(p13.1) but seemed to eradicate the difference in outcome for patients with or without t(4;14). There was no difference in the prognostic impact of del(13q) between RIC and ASCT. Similar results have been seen in the EBMT (European Group for Blood and Marrow Transplantation) study comparing ASCT and tandem ASCT/RIC [83].

Further studies are needed to determine the correct role of allogeneic transplantation in MM. The indication that patients with certain chromosomal abnormalities might fare comparatively better with allogeneic transplantation than with other types of treatment might help in the selection of patients for this treatment.

Novel agents

The so-called novel agents, proteasome inhibitors and immunomodulatory drugs used in the treatment of MM (bortezomib, thalidomide and lenalidomide), were developed as anti-tumour drugs and not as rational molecular-targeted therapy. Although sometimes a remarkable outcome is seen, these drugs do not directly target the product generated by the genetic abnormality (in contrast to imatinib in the treatment of chronic myelocytic leukaemia). Data on the prognostic impact of chromosomal aberrations in patients treated with the novel agents are usually generated through subanalysis of large clinical trials without prospective randomization based on the cytogenetic profile.

Despite the fact that del(13q) has little or no impact on outcome, according to multivariate analysis of large studies employing conventional treatment, del(13q) is the most studied aberration with regard to treatment with novel drugs. Two studies of patients with relapsed or progressive MM (SUMMIT and APEX trials), using bortezomib alone or in combination with dexamethasone, showed no clear survival advantage for patients without del(13q) when compared to those with the aberration [86]. Sagaster et al. [87] demonstrated similar findings. This is probably also true in newly diagnosed patients, as shown by San Miguel et al. [88] in the VISTA trial despite the small number of patients with del(13q) included in the analysis. Altogether, these results demonstrate that bortezomib may overcome some of the potential poor impact associated with del(13q).

By contrast, maintenance with thalidomide after ASCT did not confer any significant advantage in terms of OS of patients carrying del(13q) [89]. In the large MRC Myeloma IX study, in which cytogenetic data were available for 60% of all patients, thalidomide used in a combination regimen as first-line treatment (cyclophospahamide, thalidomide and dexamethasone; CTD) or as maintenance did not increase OS in patients with high-risk cytogenetics (t(4;14), t(14;16), t(14;20), del(1p), amp(1q) and del(17p)); on the contrary, it probably shortened the OS of these patients [90].

Lenalidomide may overcome the eventual negative impact of del(13q) on OS by reducing the relapse rate [91]. In addition, t(4;14) did not influence OS, but OS was significantly shorter in patients with del(17p) [91]. San Miguel et al. [88] showed that regimens including bortezomib (bortezomib (velcade), melphalan and prednisolone; VMP) may overcome high-risk cytogenetic profiles (t(4;14), t(14;16) and del(17p)) in newly diagnosed patients, but the number of patients in their study was small (26 and 142 with and without high-risk profiles, respectively).

Thus, there is evidence that MM patients with t(4;14) benefit from bortezomib. There is also growing evidence that lenalidomide might have the same effect, in contrast to thalidomide which should be avoided in patients with high-risk cytogenetics.

Conclusions

Knowledge regarding the chromosomal aberrations in MM has been advancing in the last decades, but there still is no known clear primary event [92]. The most prevalent aberrations involve mutation of the TP53 tumour suppressor gene, which is also the most common genetic alteration in other human cancers. Aberrations of this gene are the most predictive molecular markers for resistance to therapy and short OS. The prognosis for the group of MM patients with del(p17), (TP53), is clearly worse than the prognosis for patients with any of the other established unfavourable chromosomal abnormalities, regardless of therapy including allogeneic transplantation [65]. Developing new drugs targeting the p53 pathway may be a way to improve treatment of these patients. The negative impact of del(13q) and t(4;14) on OS may partly be neutralized by the use of novel agents or allogeneic stem cell transplantation as shown by subanalyses of large clinical trials.

Conventional karyotype analysis is only informative in 30% of cases because of the difficulty in generating metaphases within the MM tumour clone. This difficulty is explained by a low rate of proliferation of the plasma cells (PCs) and in some cases a low percentage of PCs in bone marrow samples [93, 94]. Analysis methods that are not dependent upon obtaining metaphases identify aberrations in almost all cases examined [95]. In clinical practice, the optimal method to detect chromosomal aberrations in MM is interphase FISH. This method is not yet fully validated against conventional cytogenetics, but with the use of multiple probe sets for the analysis of MM samples, FISH will allow a global vision of chromosomal aberrations and will also detect ploidy. Another advantage is that it identifies karyotypic abnormalities even in nondividing cells. FISH should be run on CD138+/CD38+ purified PCs because of the generally low percentage of PCs in MM bone marrow samples [96]. M-FISH (Fig. 2) is another method for karyotyping complex metaphases. This analysis has the advantage of allowing quicker recognition of marker chromosomes and cryptic translocations. As for traditional cytogenetics in MM, the disadvantage is the difficulty in obtaining metaphases.

Figure 2.

M-FISH analysis. A complex karyotype with both numerical and structural aberrations is shown: trisomies of chromosome numbers 1, 2, 3, 9, 11 and 21; monosomies for numbers 8, 17 and X; lack of Y; and structural aberration of numbers 2, 3, 9 and 18 as well as an undefined marker chromosome (A).

Chromosome analysis using these methods is currently the most important tool to assess risk and predict outcome in MM. With the development of new treatment modalities – new drugs in combinations with alternative transplantation modalities or in new combinations without transplantation – chromosome analyses will probably be even more important for selection of the best treatment for individual patients. Chromosome analysis should be performed in all patients with MM.

Conflict of interest statement

No conflict of interest to declare.

Acknowledgements

This study was supported by grants from the Swedish Cancer Fund and the Cancer Society in Stockholm.

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