Occurrence of dysregulated oncogenes in primary plasma cells representing consecutive stages of myeloma pathogenesis: indications for different disease entities

DNA methylation inhibition in myeloma: Experience from a phase 1b study of low-dose continuous azacitidine in combination with lenalidomide and low-dose dexamethasone in relapsed or refractory multiple myeloma

The DNA methyltransferase inhibitor azacytidine (aza) may reactivate pathways associated with plasma cell differentiation, cell cycle control, apoptosis, and immune recognition and thereby restore sensitivity to lenalidomide (len) and dexamethasone (dex) in relapsed and/or refractory multiple myeloma (RRMM). We aimed to develop an aza regimen that reaches epigenetically active levels 8 times in 28 days with less bone marrow toxicity than the myeloid malignancy standard of 7 consecutive doses to enable safe combination with len. Aza was escalated from 30 mg/m² once a week up to a predefined maximum of 50 mg/m² twice a week in combination with GFR-adjusted len (≥ 60 mL/min: 25 mg, 3059 mL/min: 10 mg) day 1 to 21 every 28 days and dex 40 mg once a week followed by a limited expansion study to a total N of 23 at the highest tolerated dose. Fifty-one patients (pts) with RRMM were screened, 42 were treated and 41 were evaluable for response based on at least 1 response assessment or progression after treatment start. The median number of prior lines of therapy was 5 (1-11) and 81% (34) were refractory to len and/or pomalidomide (pom). Two DLTs occurred in different cohorts, 1 neutropenic fever in 1/6 pts on the aza 40 mg/m² twice a week GFR ≥ 60 mL/min cohort and 1 GGT elevation in 1/6 pts on the aza 50 mg/m² GFR 30-59 mL/min cohort. An MTD was not reached and aza 50 mg/m² SC twice a week was chosen for the expansion study. At least possibly related Grade 3/4 AEs occurred in 28 pts (67%) with the following in > 1 pt: neutropenia (N = 16, 38%), anemia (N = 6, 14%), lymphopenia (N = 5, 12%), thrombocytopenia (N = 4, 10%), leukopenia (N = 4, 10%), febrile neutropenia (N = 4, 10%), fatigue (N = 3, 7%), fever (N = 2, 5%), and infection (N = 2, 5%). At a median follow up time for alive pts of 60.2 months (range: 36.1-82.5 months), the overall response rate (≥ partial response) and clinical benefit response rate (≥ minor response) was 22 and 32%, respectively, with 4 very good partial responses (10%), 5 partial responses (12%), and 4 minor responses (10%). The median PFS was 3.1 months (95% confidence interval [CI]: 2.1-5.1 months), median TTP 2.7 months (95% CI: 2.1-7.5 months), and median OS 18.6 months (95% CI: 12.9-33.0 months). Achieving at least minor response and reaching TTP > 6 months was associated with approximately 35% lower median plasma levels of the enzyme that inactivates aza, plasma cytidine deaminase (CDA, P< .0001). Two of the len refractory pts achieved longer disease control than with any prior regimen and 1 responded immediately after progression on len, bortezomib, and prednisone. Analyses of the methylation state of over 480,000 CpG sites in purified myeloma cells at screening were possible in 11 pts and on day 28 in 8 of them. As in other studies, the majority of differentially methylated CpGs compared to normal plasma cells were hypomethylated in myeloma. Treatment decreased the number of CpGs that were differentially methylated in normal plasma cells by > 0.5% in 6 and by > 5% in 3 of the 8 pts, most pronounced in 2 pts with clinically convincing aza contribution who achieved a reduction in overall differentially methylated CpGs by 23 and 68%, respectively, associated with increased expression of immunoglobulin genes. The study demonstrated tolerability of twice a week SC aza at 50 mg/m² with len and dex in RRMM and suggested aza may help overcome the len/pom refractory state, possibly by activating differentiation pathways. Relatively low response rates and association of clinical benefit with low plasma levels of the aza inactivating enzyme CDA suggest the aza regimen will need to be optimized further and pt selection may be required to maximize benefit.

A multiple myeloma classification system that associates normal B-cell subset phenotypes with prognosis

Despite the recent progress in treatment of multiple myeloma (MM), it is still an incurable malignant disease, and we are therefore in need of new risk stratification tools that can help us to understand the disease and optimize therapy. Here we propose a new subtyping of myeloma plasma cells (PCs) from diagnostic samples, assigned by normal B-cell subset associated gene signatures (BAGS). For this purpose, we combined fluorescence-activated cell sorting and gene expression profiles from normal bone marrow (BM) Pre-BI, Pre-BII, immature, naïve, memory, and PC subsets to generate BAGS for assignment of normal BM subtypes in diagnostic samples. The impact of the subtypes was analyzed in 8 available data sets from 1772 patients' myeloma PC samples. The resulting tumor assignments in available clinical data sets exhibited similar BAGS subtype frequencies in 4 cohorts from de novo MM patients across 1296 individual cases. The BAGS subtypes were significantly associated with progression-free and overall survival in a meta-analysis of 916 patients from 3 prospective clinical trials. The major impact was observed within the Pre-BII and memory subtypes, which had a significantly inferior prognosis compared with other subtypes. A multiple Cox proportional hazard analysis documented that BAGS subtypes added significant, independent prognostic information to the translocations and cyclin D classification. BAGS subtype analysis of patient cases identified transcriptional differences, including a number of differentially spliced genes. We identified subtype differences in myeloma at diagnosis, with prognostic impact and predictive potential, supporting an acquired B-cell trait and phenotypic plasticity as a pathogenetic hallmark of MM.

The myeloma stem cell concept, revisited: from phenomenology to operational terms

The concept of the myeloma stem cell may have important therapeutic implications, yet its demonstration has been hampered by a lack of consistency in terms and definitions. Here, we summarize the current documentation and propose single-cell in vitro studies for future translational studies. By the classical approach, a CD19^-/CD45^low/-/CD38^high/CD138⁺ malignant plasma cell, but not the CD19⁺/CD38^low/- memory B cell compartment, is enriched for tumorigenic cells that initiate myeloma in xenografted immunodeficient mice, supporting that myeloma stem cells are present in the malignant PC compartment. Using a new approach, analysis of c-DNA libraries from CD19⁺/CD27⁺/CD38^- single cells has identified clonotypic memory B cell, suggested to be the cell of origin. This is consistent with multiple myeloma being a multistep hierarchical process before or during clinical presentation. We anticipate that further characterization will require single cell geno- and phenotyping combined with clonogenic assays. To implement such technologies, we propose a revision of the concept of a myeloma stem cell by including operational in vitro assays to describe the cellular components of origin, initiation, maintenance, and evolution of multiple myeloma. These terms are in accordance with recent (2012) consensus statements on the definitions, assays, and nomenclature of cancer stem cells, which is technically precise without completely abolishing established terminology. We expect that this operational model will be useful for future reporting of parameters used to identify and characterize the multiple myeloma stem cells. We strongly recommend that these parameters include validated standard technologies, reproducible assays, and, most importantly, supervised prospective sampling of selected biomaterial which reflects clinical stages, disease spectrum, and therapeutic outcome. This framework is key to the characterization of the cellular architecture of multiple myeloma and its use in precision medicine.

Impact of C-Myc gene-related aberrations in newly diagnosed myeloma with bortezomib/dexamethasone therapy

Recent studies have suggested that c-Myc over-expression may be a factor indicating poor prognosis in multiple myeloma (MM), although c-Myc gene-related abnormalities, including translocation and gene amplification, have not been fully investigated in the novel agent era. Additional chromosome 8 may be considered as aggressive disease in the 1990s. To clarify the impact of these aberrations, we retrospectively analyzed newly diagnosed MM (NDMM) and relapsed/refractory MM (RRMM) with bortezomib and dexamethasone induction therapy. In the present study, the high-risk group was defined as having at least one of the following present: non-hyperdiploidy, IgH/FGFR3, and del p53. Forty NDMM cases were analyzed. At the median follow-up duration of 14.1 months, 14 RRMM were recognized. The proportions of patients in the high-risk, c-Myc gene-related aberrations, and additional chromosome 8 groups at diagnosis were 45.5, 22.5, and 10 %, respectively. The proportions of patients who developed RRMM in the high-risk, c-Myc gene-related aberrations, and additional chromosome 8 groups were 41.7, 77.7, and 50 %, respectively. Furthermore, patients with c-Myc gene-related abnormalities tended to exhibit inferior progression-free survival (PFS), and those with c-Myc gene-related abnormalities and/or additional chromosome 8 showed statistically shorter PFS. Therefore, c-Myc gene-related abnormalities and additional chromosome 8 may be related to a poorer prognosis.

RSK2(Ser227) at N-terminal kinase domain is a potential therapeutic target for multiple myeloma

Multiple myeloma is an entity of cytogenetically and genetically heterogenous plasma cell neoplasms. Despite recent improvement in the treatment outcome of multiple myeloma by novel molecular-targeted chemotherapeutics, multiple myeloma remains incurable. The identification of a therapeutic target molecule in which various signaling for cell-survival converge is a core component for the development of new therapeutic strategies against multiple myeloma. RSK2 is an essential mediator of the ERK1/2 signaling pathway for cell survival and proliferation. In this study, we discovered that RSK2(Ser227), which is located at the N-terminal kinase domain and is one site responsible for substrate phosphorylation, is activated through phosphorylation regardless of the type of cytogenetic abnormalities or upstream molecular signaling in all 12 multiple myeloma-derived cell lines examined and 6 of 9 patient-derived CD138-positive primary myeloma cells. The chemical inhibition of RSK2(Ser227) by BI-D1870 or gene knockdown of RSK2 inhibits myeloma cell proliferation through apoptosis induction, and this anti-myeloma effect was accompanied by downregulation of c-MYC, cyclin D, p21(WAF1/CIP1), and MCL1. RSK2(Ser227) inhibition resulting from BI-D1870 treatment restored lenalidomide-induced direct cytotoxicity of myeloma cells from interleukin-6-mediated cell protection, showed no cross-resistance to bortezomib, and exerted additive/synergistic antiproliferative effects in conjunction with the mTOR, histone deacetylase, and BH3-mimicking BCL2/BCLX(L) inhibitors. These results suggest that RSK2(Ser227) is a potential therapeutic target not only for newly diagnosed but also for patients with later phase multiple myeloma who are resistant or refractory to currently available anti-myeloma therapies.

Identification of translocation products but not K-RAS mutations in memory B cells from patients with multiple myeloma

BACKGROUND

Several laboratories have shown that cells with a memory B-cell phenotype can have the same clonotype as multiple myeloma tumor cells.

DESIGN AND METHODS

The aim of this study was to determine whether some memory B cells have the same genetic alterations as their corresponding multiple myeloma malignant plasma cells. The methodology included sorting multiple myeloma or memory B cells into RNA stabilizing medium for generation of subset-specific polymerase chain reaction complementary DNA libraries from one or 100 cells.

RESULTS

Cells with the phenotype of tumor plasma cells (CD38(++)CD19(-)CD45(-/+)CD56(-/+/++)) or memory B cells (CD38(-)/CD19(+)/CD27(+)) were isolated by flow activated cell sorting. In samples from all four patients with multiple myeloma and from two of the three with monoclonal gammopathy of undetermined significance, we identified memory B cells expressing multiple myeloma-specific oncogenes (FGFR3; IGH-MMSET; CCND1 high) dysregulated by an IGH translocation in the respective tumor plasma cells. By contrast, in seven patients with multiple myeloma, each of whom had tumor plasma cells with a K-RAS61 mutation, a total of 32,400 memory B cells were analyzed using a sensitive allele-specific, competitive blocker polymerase chain reaction assay, but no K-RAS mutations were identified.

CONCLUSIONS

The increased expression of a specific "early" oncogene of multiple myeloma (monoclonal gammopathy of undetermined significance) in some memory B cells suggests that dysregulation of the oncogene occurs in a precursor B-cell that can generate memory B cells and transformed plasma cells. However, if memory B cells lack "late" oncogene (K-RAS) mutations but express the "early" oncogene, they cannot be involved in maintaining the multiple myeloma tumor, but presumably represent a clonotypic remnant that is only partially transformed.

Regulation of the CD56 promoter and its association with proliferation, anti-apoptosis and clinical factors in multiple myeloma

Multiple myeloma (MM) is an incurable B-cell malignancy characterised by uncontrolled growth and accumulation of malignant plasma cells in the bone marrow. Aberrant expression of CD56 in patients with MM is thought to contribute to a worsened disease course and metastasis. We therefore investigated the regulation of the CD56 promoter in relation to typical clinical factors. We used qPCR and FACS to measure the expression levels of CD56, and potential regulatory factors in patients with MM and related these with MM progression/prognosis. The transcription factors BTBD3, Pax5, RUNX1 and MMSET were positively associated with CD56 expression, as was CYCLIN D1, which is involved in disease progression, anti-apoptosis and proliferation. RUNX1 was negatively associated with the survival of stem-cell transplanted patients. Our findings propose four potential activators of the CD56 promoter and for CD56 to be involved in proliferation and anti-apoptosis, leading to disease progression in MM.

Myeloma cell expression of 10 candidate genes for osteolytic bone disease. Only overexpression of DKK1 correlates with clinical bone involvement at diagnosis

Osteolytic bone disease (OBD) in multiple myeloma (MM) is caused by interactions between MM cells and the bone marrow microenvironment and is characterized by increased osteoclastic bone resorption and decreased osteoblastic bone formation. Recently, the role of osteoblast inhibition has come into focus, especially the possible role of overexpression of DKK1, an inhibitor of the Wnt signalling pathway. Further, CKS2, PSME2 and DHFR have also been reported as candidate genes for OBD. We studied the gene expression by quantitative reverse transcription polymerase chain reaction of TNFSF11 (RANKL), TNFSF11A (RANK), TNFRSF11B (OPG), CCL3 (MIP1A), CCL4 (MIP1B), PTHR1 (PTHrp), DKK1, CKS2, PSME2 and DHFR in purified, immunophenotypic FACS-sorted plasma cells from 171 newly diagnosed MM patients, 20 patients with monoclonal gammopathy of undetermined significance and 12 controls. The gene expressions of the analysed genes were correlated with radiographically assessed OBD. Only overexpression of DKK1 was correlated to the degree of OBD. Myeloma cells did not express TNFSF11A, TNFSF11, or TNFRSF11B, and very rarely expressed CCL3 and PTHR11. CCL4, CKS2, PSME2 and DHFR were variably expressed, but the expression of these genes showed no correlation with OBD. In contrast, loss of PSME2 expression in MM plasma cells was significantly correlated with OBD.

Dysregulation ofCD47and the ligands thrombospondin 1 and 2 in multiple myeloma

CD47 and thrombospondin 1 and 2 (TSP1 and TSP2) expression were analysed by real-time reverse transcription polymerase chain reaction in fluorescence-activated cell sorted plasma cells (PCs) from patients at consecutive stages of multiple myeloma (MM) development. 80% of MM patients, but only 39% of patients with monoclonal gammopathy of undetermined significance (MGUS) expressed CD47; median expression level increased 10-fold with progression from MGUS to MM. Elevated TSP1/TSP2 levels occurred in bone marrow cultures from MM patients compared with healthy donors. CD47 and TSP1/TSP2 may have a potential role in the pathophysiology of MM, probably in the interaction between MM PCs and the microenvironment.

Ten years and counting: so what do we know about t(4;14)(p16;q32) multiple myeloma

Multiple myeloma is a genetically heterogenous disease with a wide variety of characterized genetic aberrations. Until recently, the impact of these aberrations on patient outcome was not known. However, in the last 5-10 years, several genetic markers have been linked to patient outcome. One of the strongest predictors of outcome identified to date is t(4;14)(p16;q32). Although this translocation is tightly linked to chromosome 13 deletions, another poor prognosis marker, it is becoming apparent that the translocation and not the deletion of 13 is the important factor. Unfortunately, despite the known association with outcome, an understanding of the mechanism(s) whereby the translocation contributes to developing and maintaining this aggressive form of myeloma remains elusive.

Toll-like receptors mediate proliferation and survival of multiple myeloma cells

Multiple myeloma (MM) is an incurable B-cell malignancy characterized by accumulation of malignant plasma cells in bone marrow (BM) and recurrent or persistent infections. Toll-like receptors (TLRs) are essential in the host defense against infections and today 10 human TLRs (TLR1-TLR10) and one TLR-homolog (RP105) have been characterized. B cells express several TLRs (mainly TLR1, 6, 7, 9, 10 and RP105) and TLR-initiated responses in B cells include proliferation, anti-apoptosis effect and plasma cell (PC) differentiation. The present study was designed to analyze the role of TLRs in MM. We show that frequent expressions of TLRs were detected in cell lines from MM patients (minimum six TLRs in each). In comparison, only few TLRs (mainly TLR1 and or RP105) were found expressed in PCs from BM of healthy donors. In addition, TLR-specific ligands induce increased proliferation and survival of the MM cell lines, partially due to an autocrine interleukin-6 production. Importantly, we demonstrate that also PC from MM patients proliferates in response to TLR-specific ligands. In conclusion, TLR-ligands may contribute to increased growth and survival of MM cells in MM patients.

Serum YKL-40 concentrations in newly diagnosed multiple myeloma patients and YKL-40 expression in malignant plasma cells

OBJECTIVES

A potential role in cancer biology is suggested for YKL-40 (CHI3L1, HC gp-39). The purpose of this study was to evaluate the clinical value of serum YKL-40 (sYKL-40) in multiple myeloma (MM) and to examine YKL-40 expression in malignant plasma cells (MM PCs).

METHODS

sYKL-40 was measured by enzyme-linked immunosorbent assay (ELISA) in 82 patients with newly diagnosed MM. YKL-40 expression in immunophenotypically defined plasma cells was investigated by double-labelled immunohistochemistry in 21 MM patients and by real-time reverse transcriptase polymerase chain reaction (RT-PCR) in cDNA archives generated by global RT-PCR in seven controls, 14 patients with monoclonal gammopathy of undetermined significance (MGUS), 45 MM patients, nine patients with extramedullary myeloma (exMM), and seven human myeloma cell lines (HMCLs).

RESULTS

sYKL-40 was elevated above a constructed reference range for healthy controls in 29% of the patients investigated. Patients with elevated sYKL-40 had reduced overall survival and event-free survival when compared to patients with normal sYKL-40, but sYKL-40 level was defeated by beta(2)-microglobulin in the multivariate analyses. Intramedullary MM PCs lacked significant expression of YKL-40, but high levels of YKL-40 expression were seen in extramedullary MM PCs from one exMM patient and in six HMCLs. Further investigations of other bone marrow (BM) cells showed YKL-40 expression in megakaryocytes, neutrophils and adherent cells from long-term BM cultures.

CONCLUSIONS

In newly diagnosed MM-patients, a sYKL-40 elevated above the reference range predicts a poor clinical outcome, and YKL-40 is expressed by other BM cells than MM PCs. At this point, routine measurements of sYKL-40 are not warranted, but YKL-40 should be considered as a potential player in the pathophysiology of MM.

Plasma cell tumour progression in iMycEmu gene-insertion mice

The authors have recently reported that gene-targeted iMyc(Emu) mice that carry a His(6)-tagged mouse Myc cDNA, Myc(His), just 5' of the immunoglobulin heavy-chain enhancer, Emu, are prone to 'spontaneous' neoplasms of the B-lymphocyte lineage. The present study has used histological, immunohistochemical, and molecular genetic methods to investigate a subset of these neoplasms referred to as extraosseous plasmacytomas (PCTs). It is shown that 20.8% (20/96) of tumour-bearing iMyc(Emu) mice on a mixed genetic background of segregating C57BL/6 and 129/SvJ alleles develop PCT by 500 days. The Myc(His)-induced PCTs produced monoclonal immunoglobulin and developed in the gut-associated lymphoid tissue (GALT), particularly the mesenteric node and Peyer's patches. The PCTs overexpressed Myc(His), at the expense of normal Myc, and exhibited gene expression changes on cDNA macroarrays that were consistent with Myc(His)-driven neoplasia. Surprisingly, in one of three PCT-derived cell lines, Myc(His) was 'replaced' by a naturally occurring T(12;15) translocation, which changed the mode of Myc deregulation from gene insertion (Myc(His) transgene) to chromosomal translocation (juxtaposition of normal Myc to the immunoglobulin heavy-chain locus Igh). These findings provide evidence that recreation of the mouse PCT-associated T(12;15)(Igh(Emu)-Myc) translocation by gene insertion in mice results in the predictable development of PCTs in approximately one-fifth of the tumour-bearing mice. Myc(His)-driven PCTs recapitulate aspects of human plasma cell neoplasms, for which relatively few models exist in mice. For example, PCT development in the iMyc(Emu) mice may provide a good system to study the mechanism by which human MYC facilitates the progression of plasma cell myeloma (multiple myeloma) in humans.

Identification of ID-1 as a potential target gene of MMSET in multiple myeloma

The frequently detected t(4;14)(p16.3;q32) translocation in multiple myeloma (MM) results in a dysregulation of two potential oncogenes: multiple myeloma SET domain (MMSET) and fibroblast growth factor receptor 3 (FGFR3). As the expression of FGFR3 is undetectable in 30% of the t(4;14)+ MM patients, MMSET has been suggested to play an important role in the malignant transformation associated with the t(4;14) translocation. Screening with a real-time polymerase chain reaction (PCR) found complex expression patterns of the MMSET transcripts in fluorescence-activated cell sorted (FACS)-purified plasma cells (PCs) from 15 t(4;14)+ MM patients. In addition, potential target genes of MMSET type I and II were identified, using microarray analyses of MMSET transfected cell lines. Subsequently, the expression of potential target genes was verified by real-time PCR in FACS-purified PCs from 15 t(4;14)+ and 22 t(4;14)- MM patients. We suggest that the inhibitor of differentiation 1 (ID-1) is a target gene of MMSET, based on its upregulation in MMSET transfected cell lines and a significant association between the t(4;14) translocation and ID-1 expression in MM patients (P = 0.002). As high levels of ID-1 are associated with cancer, our findings indicate that MMSET promotes oncogenic transformation in t(4;14)+ MM patients by transcriptional activation of ID-1 expression.

Extraosseous IL-6 transgenic mouse plasmacytoma sometimes lacks Myc-activating chromosomal translocation

The cellular oncogene MYC and plasma cell growth, differentiation, and survival factor IL-6 play critical roles in the natural history of human plasma cell neoplasms such as multiple myeloma (MM). Myc and IL-6 also are at the center of neoplastic plasma cell transformation in BALB/c mice that carry a human IL-6 transgene and, therefore, predictably develop plasmacytomas (PCTs). We showed previously that, much like advanced MM or human myeloma cell lines (HMCLs), in which MYC is frequently deregulated in cis because of complex cytogenetic aberrations juxtaposing MYC to immunoglobulin enhancers, IL-6 transgenic PCTs commonly deregulate Myc in cis by chromosomal translocation, predominantly T(12;15)(Igh-Myc). In this article, we show that, analogous to primary MM in which MYC is mostly deregulated in trans by signaling pathways converging at the MYC promoter, IL-6 transgenic PCTs sometimes develop in the absence of Myc translocations, thus activating Myc in trans. We present cytogenetic and molecular evidence on two IL-6 transgenic PCTs that contained overexpressed Myc protein but lacked T(12;15)(Igh-Myc) and two related Myc--deregulating translocations that juxtapose Myc to immunoglobulin light-chain instead of heavy-chain enhancers: T(6;15)(Igkappa-Pvt1) and T(15;16)(Pvt1-Iglambda). We conclude that Myc translocations are not strictly required for IL-6-driven PCT development in mice. IL-6 transgenic PCTs may provide a valuable model system for elucidating both trans and cis mechanisms of Myc deregulation of great relevance for MYC deregulation in human MM.

Gene expression profiling of plasma cell dyscrasias reveals molecular patterns associated with distinct IGH translocations in multiple myeloma

Multiple myeloma (MM) is the most common form of plasma cell dyscrasia, characterized by a marked heterogeneity of genetic lesions and clinical course. It may develop from a premalignant condition (monoclonal gammopathy of undetermined significance, MGUS) or progress from intramedullary to extramedullary forms (plasma cell leukemia, PCL). To provide insights into the molecular characterization of plasma cell dyscrasias and to investigate the contribution of specific genetic lesions to the biological and clinical heterogeneity of MM, we analysed the gene expression profiles of plasma cells isolated from seven MGUS, 39 MM and six PCL patients by means of DNA microarrays. MMs resulted highly heterogeneous at transcriptional level, whereas the differential expression of genes mainly involved in DNA metabolism and proliferation distinguished MGUS from PCLs and the majority of MM cases. The clustering of MM patients was mainly driven by the presence of the most recurrent translocations involving the immunoglobulin heavy-chain locus. Distinct gene expression patterns have been found to be associated with different lesions: the overexpression of CCND2 and genes involved in cell adhesion pathways was observed in cases with deregulated MAF and MAFB, whereas genes upregulated in cases with the t(4;14) showed apoptosis-related functions. The peculiar finding in patients with the t(11;14) was the downregulation of the alpha-subunit of the IL-6 receptor. In addition, we identified a set of cancer germline antigens specifically expressed in a subgroup of MM patients characterized by an aggressive clinical evolution, a finding that could have implications for patient classification and immunotherapy.

Characterization of oncogene dysregulation in multiple myeloma by combined FISH and DNA microarray analyses

Chromosomal translocations involving the immunoglobulin heavy chain (IGH) locus and various partner loci frequently are associated with multiple myeloma (MM). We investigated the expression profiles of the FGFR3/MMSET, CCND1, CCND3, MAF, and MAFB genes, which are involved in t(4;14)(p16.3;q32), t(11;14)(q13;q32), t(6;14)(p21;q32), t(14;16)(q32;q23), and t(14;20)(q32;q12), respectively, in purified plasma cell populations from 39 MMs and six plasma cell leukemias (PCL) by DNA microarray analysis and compared the results with the presence of translocations as assessed by dual-color FISH or RT-PCR. A t(4;14) was found in 6 MMs, t(11;14) in 9 MMs and 1 PCL, t(6;14) in 1 MM, t(14;16) in 2 MMs and 1 PCL, and t(14;20) in 1 PCL. In all cases, the translocations were associated with the spiked expression of target genes. Furthermore, gene expression profiling enabled the identification of putative translocations causing dysregulation of CCND1 (1 MM and 1 PCL) and MAFB (1 MM and 1 PCL) without any apparent involvement of immunoglobulin loci. Notably, all of the translocations were mutually exclusive. Markedly increased MMSET expression was found in 1 MM showing associated FGFR3 and MMSET signals on an unidentified chromosome. Our data suggest the importance of using combined molecular cytogenetic and gene expression approaches to detect genetic aberrations in MM.

Possible roles for activating RAS mutations in the MGUS to MM transition and in the intramedullary to extramedullary transition in some plasma cell tumors

To assess a possible role in tumor progression, the occurrence and type of K- and N-RAS mutations were determined in purified tumor cells, including samples from patients with premalignant monoclonal gammopathy of undetermined significance (MGUS), multiple myeloma (MM), and extramedullary plasma cell (PC) tumors (ExPCTs). Immunophenotypic aberrant PCs were flow sorted from 20 MGUS, 58 MM, and 13 ExPCT patients. One RAS mutation was identified in 20 MGUS tumors (5%), in contrast to a much higher prevalence of RAS mutations in all stages of MM (about 31%). Further, oncogene analyses showed that RAS mutations are not evenly distributed among different molecular subclasses of MM, with the prevalence being increased in MM-expressing cyclin D1 (P = .015) and decreased in MM with t(4;14) (P = .055). We conclude that RAS mutations often provide a genetic marker if not a causal event in the evolution of MGUS to MM. Surprisingly, RAS mutations were absent in bone marrow tumor cells from all patients with ExPCT, a result significantly different from intramedullary MM (P = .001). From 3 of 6 patients with paired intramedullary and extramedullary PCs and identical immunoglobulin heavy chain gene (IgH) sequences, RAS mutations were identified only in extramedullary PCs, suggesting a role for RAS mutations in the transition from intramedullary to extramedullary tumor.