Nonrandom chromosomal imbalances in primary mediastinal b-cell lymphoma detected by arbitrarily primed PCR fingerprinting

Malignant hematopoietic cell lines: in vitro models for the study of primary mediastinal B-cell lymphomas

Primary mediastinal B-cell lymphoma (PMBL) is a highly aggressive disease with a unique set of biological, clinical, morphological, immunological and in particular genetic features that in the molecular era of defining lymphomas clearly distinguishes it as a separate entity from other diffuse large B-cell lymphomas (DLBCL). A precise molecular diagnosis of PMBL can be achieved by gene expression profiling. The signature gene expression profile of PMBL is more closely related to classic Hodgkin lymphoma (cHL) than to other DLBCL subgroups. A number of common genetic aberrations in PMBL and cHL further underscore their close relationship. To investigate the pathobiology of lymphomas in depth, many groups have turned to cell lines that are suitable models facilitating molecular studies and providing unique insights. For the purposes of the current perspective, we focus on four bona fide PMBL-derived cell lines (FARAGE, KARPAS-1106, MEDB-1, U-2940) that we identified and validated as such through hierarchical cluster analysis among a large collection of leukemia-lymphoma cell lines. These gene expression profiles showed that the four PMBL cell lines represent a distinct entity and are most similar to cHL cell lines, confirming derivation from a related cell type. A validated cell line resource for PMBL should assist those seeking druggable targets in this entity. This review aims to provide a comprehensive overview of the currently available cellular models for the study of PMBL.

Mutations and chromosomal rearrangements of JAK2: not only a myeloid issue

Until today, JAK2 alterations have been mainly associated with myeloid malignancies among which they play a key pathogenic role in chronic myeloproliferative neoplasms. More recently, aberrations involving the JAK2 gene have also been reported in lymphoid diseases, including acute leukemia and lymphomas. In addition, the constitutively activating JAK2V617F mutation has been identified in some patients affected by B-chronic lymphocytic leukemia with a concomitant myeloproliferative neoplasm. Interestingly, these cases could help us to better understand the pathogenesis of these myeloid and lymphoid diseases and reveal if they share a common ancestral progenitor or just coincide. The involvement of JAK2 in lymphoid neoplasms may suggest the possibility of new therapeutic approaches broadening the use of JAK1-2 inhibitors also to these malignancies.

Primary mediastinal B-cell lymphoma: treatment and therapeutic targets

Primary mediastinal B-cell lymphoma (PMBCL) is a recognised subtype of diffuse large B-cell lymphoma according to the WHO classification that represents approximately 5% of aggressive lymphomas, and 2% of all cases of lymphomas. It presents with unique clinical, morphologic and immunophenotypic characteristics that define the disease. Retrospective studies have found that PMBCL patients have excellent survival rates with a distinct plateau and a trend to better outcome if treated with dose-intensified chemotherapy with MACOPB or VACOPB. In spite of the multiple molecular data known, generated on the pathogenesis of this tumour, treatment is still essentially based on a combination of chemo and immunotherapy. We take this opportunity for reviewing the recent biologic data provided by gene expression profiling of the tumour, for discussing new potential therapeutic targets.

Chromosomal instability in gastric mucosa-associated lymphoid tissue lymphomas: a fluorescent in situ hybridization study using a tissue microarray approach

Extranodal marginal zone B-cell lymphomas (mucosa-associated lymphoid tissue [MALT] lymphomas) of the gastrointestinal tract have been known to have characteristic chromosomal aberrations including trisomies of chromosomes 3, 12, and 18. However, knowledge of the clinical significance of cytogenetic changes in MALT lymphomas is still limited. In the present study, the frequency of the numeric and structural aberrations of the chromosomes 1, 3, 12, 18 and X and of the MALT1 gene as well as their potential clinical significance were analyzed by using fluorescent in situ hybridization on a tissue microarray containing 257 tissue samples from 203 cases of surgically resected primary gastric lymphomas including 115 cases of MALT lymphomas, 88 cases of diffuse large B-cell lymphomas (DLBCLs, 75 with an associated MALT lymphoma, so-called ex-MALT DLBCL, and 13 de novo), and 54 controls cases of Helicobacter pylori-associated chronic gastritis. Clinical follow-up information was available in 137 cases. Trisomies 1, 3, 12, and 18 were detected in 3.3%, 44.4%, 12.3%, and 19.2% of MALT lymphomas and in 11.1%, 42.2%, 26.5%, and 22.0% of ex-MALT DLBCLs, respectively. In addition, we found gains of the X chromosome in 36.4% of MALT lymphomas, in 34.5% of ex-MALT DLBCLs, and in 36.4% of de novo DLBCLs. Structural and/or numeric abnormalities of the MALT1 gene were observed in 37.0% of MALT lymphomas and in 22.2% of ex-MALT DLBCLs. In de novo DLBCL, trisomies for chromosomes 3, 12, 18, and X were found in 42.9%, 10.0%, 11.1%, and 36.4%, respectively, whereas alterations of MALT1 (namely, translocations) were found in 20.0% of the cases. An unexpected high and previously unreported gain of chromosome X in gastric MALT lymphomas was found. This tumor appears, therefore, to be a genetically unstable neoplasia. Our results point out that t(11;18) and aneuploidy may be both involved in lymphomagenesis and that at least a subset of MALT lymphomas may progress toward high-grade neoplasia.

Primary Mediastinal B-Cell Lymphoma

Primary mediastinal B-cell lymphoma is a discrete clinicopathologic entity. Molecular analysis reveals it to be distinct from other types of large B-cell lymphoma, and retrospective analysis suggests that it may respond better to multi-agent chemotherapy regimens than to the more commonly used CHOP. The addition of rituximab may mitigate such differences, and may also diminish the role of consolidation radiotherapy, which is often used to treat residual mediastinal masses. For the future the role of FDG-PET scanning requires prospective examination, and it is hoped that this may allow the de-escalation of treatment if it can be shown to yield reliable prognostic information. The relative rarity of this type of lymphoma necessitates international collaboration in clinical trials, with a prospective clinicopathologic study, IELSG 26, already underway.

Frequent occurrence of deletions in primary mediastinal B-cell lymphoma

Primary mediastinal B-cell lymphoma (PMBCL) is a distinct subtype of diffuse large B-cell lymphoma. PMBCL has been previously studied with a variety of genomic techniques resulting in frequent detection of chromosomal gains; however, chromosomal losses have been rarely reported. This finding contrasts many other types of lymphoma, in which deletions are common. We hypothesize that segmental losses do exist but may have escaped detection by methods used in the previous studies. Using array comparative genomic hybridization to a tiling-resolution microarray encompassing the entire human genome, PMBCL samples were analyzed for genomic copy number alterations. An almost equal number of gains and losses of chromosomal material were detected throughout the genome (216 vs. 193, respectively). A selection of these DNA copy number alterations were confirmed by quantitative real-time PCR. Recurrent gains were detected at all previously reported regions of gain, including 9p seen in approximately 70% of cases. Recurrent chromosomal losses were observed at 1p, 3p, 4q, 6q, 7p, and 17p, with a novel event at 1p13.1-p13.2 representing the most frequent at 42% of cases analyzed. We conclude that consistent losses are present in the PMBCL genome. Given the similar frequency of losses to that of segmental gains of DNA, they are likely to play an important role in the pathogenesis of PMBCL.

Das mediastinale (thymische) großzellige B-Zell-Lymphom

Mediastinal B-cell lymphoma is a locally highly aggressive tumour which was first described in the early 1980s. The incidence is about 2-3% of all non-Hodgkin's lymphomas. The conceptional evolution of this lymphoma entity was hampered by its low incidence and the broad spectrum of morphological variants present. However, since mediastinal B-cell lymphoma has distinct morphological, immunological, genetic, and clinical features, it has been listed in the revised European-American Classification of Lymphoid Neoplasms (REAL-Classification) since 1994 as a variant of diffuse large B-cell lymphoma. In the World Health Organization classification of malignant lymphomas, mediastinal B-cell lymphoma is now listed with an own disease code (ICD-9679/3).

MCT-1 protein interacts with the cap complex and modulates messenger RNA translational profiles

MCT-1 is an oncogene that was initially identified in a human T cell lymphoma and has been shown to induce cell proliferation as well as activate survival-related pathways. MCT-1 contains the PUA domain, a recently described RNA-binding domain that is found in several tRNA and rRNA modification enzymes. Here, we established that MCT-1 protein interacts with the cap complex through its PUA domain and recruits the density-regulated protein (DENR/DRP), containing the SUI1 translation initiation domain. Through the use of microarray analysis on polysome-associated mRNAs, we showed that up-regulation of MCT-1 was able to modulate the translation profiles of BCL2L2, TFDP1, MRE11A, cyclin D1, and E2F1 mRNAs, despite equivalent levels of mRNAs in the cytoplasm. Our data establish a role for MCT-1 in translational regulation, and support a linkage between translational control and oncogenesis.

Phosphorylation of MCT-1 by p44/42 MAPK is required for its stabilization in response to DNA damage

We discovered a novel oncogene in a T-cell lymphoma cell line, multiple copies in T-cell lymphoma-1 (MCT-1), that has been shown to decrease cell-doubling time, shorten the duration of G(1) transit time and/or G(1)-S transition, and transform NIH3T3 fibroblasts. We subsequently demonstrated that there were significantly increased levels of MCT-1 protein in a subset of primary diffuse large B-cell lymphomas. Levels of MCT-1 protein were shown to be increased after exposure to DNA damaging agents. This increase did not require new protein synthesis, suggesting that post-translational mechanisms were involved. Phosphorylation is one potential mechanism by which the activity of molecules involved in cell cycle/survival is rapidly modulated. The RAS/mitogen-activated/extracellular-regulated kinase (MEK)/extracellular signal-regulated kinases (ERK) pathway plays a prominent role in the regulation of cell growth and proliferation through phosphorylation-dependent regulation of several substrates. The MCT-1 protein is predicted to have numerous putative phosphorylation sites. Using a combination of genetic and pharmacological approaches, we established that phosphorylation of MCT-1 protein by p44/p42 mitogen-activated protein kinases is critical for stabilization of MCT-1 protein and for its ability to promote cell proliferation. Our data suggests that targeting the RAS/MEK/ERK signal transduction cascade may provide a potential therapeutic approach in lymphomas and related malignancies that exhibit high levels of MCT-1 protein.

The random amplified polymorphic DNA (RAPD) assay and related techniques applied to genotoxicity and carcinogenesis studies: a critical review

More than 9000 papers using the random amplified polymorphic DNA (RAPD) or related techniques (e.g. the arbitrarily primed polymerase chain reaction (AP-PCR)) have been published from 1990 to 2005. The RAPD method has been initially used to detect polymorphism in genetic mapping, taxonomy and phylogenetic studies and later in genotoxicity and carcinogenesis studies. Despite their extensive use, these techniques have also attracted some criticisms, mainly for lack of reproducibility. In the light of their widespread applications, the objectives of this review are to (1) identify the potential factors affecting the optimisation of the RAPD and AP-PCR assays, (2) critically describe and analyse these techniques in genotoxicity and carcinogenesis studies, (3) compare the RAPD assay with other well used methodologies, (4) further elucidate the impact of DNA damage and mutations on the RAPD profiles, and finally (5) provide some recommendations/guidelines to further improve the applications of the assays and to help the identification of the factors responsible for the RAPD changes. It is suggested that after proper optimisation, the RAPD is a reliable, sensitive and reproducible assay, has the potential to detect a wide range of DNA damage (e.g. DNA adducts, DNA breakage) as well as mutations (point mutations and large rearrangements) and therefore can be applied to genotoxicity and carcinogenesis studies. Nevertheless, the interpretation of the changes in RAPD profiles is difficult since many factors can affect the generation of RAPD profiles. It is therefore important that these factors are identified and taken into account while using these assays. On the other hand, further analyses of the relevant bands generated in RAPD profile allow not only to identify some of the molecular events implicated in the genomic instability but also to discover genes playing key roles, particularly in the initiation and development of malignancy. Finally, to elucidate the potential genotoxic effects of environmental contaminants, a powerful strategy could be firstly to use the RAPD assay as a screening method and secondly to apply more specific methods measuring for instance DNA adducts, gene mutations or cytogenetic effects. It is also envisaged that these assays (i.e. RAPD and related techniques), which reflect effects at whole genome level, would continue to complement the use of emerging technologies (e.g. microarrays which aim to quantify expression of individual genes).

Characterization of the MCT-1 pseudogene: identification and implication of its location in a highly amplified region of chromosome 20

The MCT-1 oncogene was initially identified as an amplified gene on chromosome Xq22-24 in a T-cell lymphoma. MCT-1 is over-expressed in a subset of diffuse large B-cell lymphoma (DLBCL), a common form of Non-Hodgkin's Lymphoma (NHL). We have identified a pseudogene for MCT-1 (PsiMCT-1) that is located on chromosome 20q11.2, a region within an amplicon containing several important genes frequently amplified in certain breast and ovarian cancers. Genomic analysis revealed that PsiMCT-1 is a processed pseudogene. Interestingly, both MCT-1 and its pseudogene are located on regions of the genome that are frequently amplified in several different human malignancies. MCT-1 is the oldest known oncogene and its insertion as a pseudogene occurred at a later time point in evolution. Existence of PsiMCT-1 should be considered when analyzing genomic amplification and or expression of MCT-1. Analysis of MCT-1 and PsiMCT-1 might provide clues to cancer genes and their evolution across species.

Expression of TP73L is a helpful diagnostic marker of primary mediastinal large B-cell lymphomas

Primary mediastinal large B-cell lymphoma is a well-defined lymphoma entity whose molecular pathogenesis is incompletely understood and also lacking well-established diagnostic markers. Recently, the presence of overlapping features between classical Hodgkin's lymphoma and primary mediastinal large B-cell lymphoma was highlighted by gene expression profiling as well as morphological studies. We investigated the expression of TP73L (commonly known as p63) isoforms in primary mediastinal large B-cell lymphoma at both protein and mRNA level, and demonstrated the exclusive presence of transactivating (TA) isoforms in all cases. We also demonstrated that TP73L is expressed in a subset of germinal center B-cells, as well as in some diffuse large B-cell lymphomas, but it is never present in classical Hodgkin lymphoma. Nodular lymphocyte predominant Hodgkin's lymphoma also showed TP73L positivity by immunohistochemistry. Isoform analysis by real-time PCR showed that TA-TP73Lalpha is the most represented in primary mediastinal large B-cell lymphoma, but TA-TP73Lgamma is the most differentially expressed in comparison to both germinal center B-cells and diffuse large B-cell lymphomas. TP73L expression proved a useful diagnostic marker of primary mediastinal large B-cell lymphoma, and gave new insights in to the molecular pathways playing a role in this lymphoma.

Biallelic mutation of SOCS-1 impairs JAK2 degradation and sustains phospho-JAK2 action in the MedB-1 mediastinal lymphoma line

Primary mediastinal B-cell lymphoma (PMBL) is a well-defined subtype of diffuse large B-cell lymphoma. Molecular cytogenetics revealed frequent gains of 9p24. JAK2, mapping in this region, is presently regarded as a candidate oncogene because expression profiling showed high Janus kinase-2 (JAK2) transcript levels and JAK2 was found to be constitutively phosphorylated in mediastinal B-cell lymphomas. We confirm that in the MedB-1 mediastinal B-cell line, harboring a trisomy 9, JAK2 transcription is elevated and the product is highly phosphorylated. However, JAK2 is not overexpressed at the protein level. On top, JAK2 protein turnover is even delayed. This unexpected finding coincides with a biallelic mutation of the suppressor of cytokine signaling-1 (SOCS-1) gene in this cell, which abrogates SOCS box function of the protein. Ectopic expression of wild-type (wt) SOCS-1 in MedB-1 leads to growth arrest and dramatic reduction of phospho-JAK2 and its downstream partner phospho-signal transducer and activator of transcription-5 (phospho-STAT5). Ultimately, the target gene cyclin D1 is repressed in transfectants while RB1, which is silenced in MedB-1, is induced. We conclude that, in MedB-1, action of phospho-JAK2 is sustained due to defective SOCS-1. Hence, SOCS-1 qualifies as a novel tumor suppressor. Of note, SOCS-1 mutations are also present in the parental tumor of MedB-1 and were detected in 9 of 20 PMBLs.

Clinicopathologic Significance and Prognostic Value of Chromosomal Imbalances in Diffuse Large B-Cell Lymphomas

Purpose

To determine the clinicopathologic significance and prognostic value of chromosomal imbalances in diffuse large B-cell lymphomas (DLBCL).

Patients and Methods

We have examined 64 tumors at diagnosis using comparative genomic hybridization and real-time quantitative polymerase chain reaction (PCR), single-stranded conformational polymorphism, and DNA sequencing for the analysis of several potential target genes.

Results

The most recurrent alterations were gains of 18q (20%), Xq (15%), 2p, 7q, and 12p (14%), and losses of 6q and 17p (14%). Frequent high-level DNA amplifications were detected at 2p13-p16 and 18q21 loci. Real-time quantitative PCR detected REL and BCL11A gene amplifications in the nine patients with gains at 2p13-p16 and only in one additional patient with normal chromosome 2. Similarly, the BCL-2 gene was amplified in the 12 tumors with gains of 18q21 but in none of 39 patients with normal 18q profile. p53 gene inactivation was detected in nine of 58 (16%) tumors and was commonly associated with 17p losses. Tumors with 18q gains were significantly associated with a high number of chromosomal imbalances, primary nodal presentation, high serum lactate dehydrogenase levels, high International Prognostic Index, shorter cause-specific survival, and a high risk of relapse. Losses of 17p and p53 gene alterations were associated with an absence of complete response achievement.

Conclusion

These results suggest that DLBCLs have a characteristic pattern of genomic alterations; 18q gains or amplifications and 17p losses are associated with particular clinicopathological features and aggressive clinical behavior. Additional studies are needed to confirm these observations in larger series of patients.

Expression of the candidate MCT-1 oncogene in B- and T-cell lymphoid malignancies

Our laboratory has recently discovered a novel candidate oncogene, MCT-1, amplified in human T-cell lymphoma and mapped to chromosome Xq22-24. This region is amplified in a subset of primary B-cell non-Hodgkin lymphoma (NHL), suggesting that increased copy number of a gene(s) located in this region confers a growth advantage to some primary human lymphomas. We examined a diverse panel of lymphoid malignancies for the expression of MCT-1. We demonstrated that there are significantly increased levels of MCT-1 protein in a panel of T-cell lymphoid cell lines and in non-Hodgkin lymphoma cell lines. Furthermore, we identified a subset of primary diffuse large B-cell lymphomas that exhibited elevated levels of MCT-1 protein. Interestingly, all transformed follicular lymphomas in our study demonstrated elevated protein levels of MCT-1. There was no detectable MCT-1 protein in leukemic cells from patients with chronic lymphocytic leukemia or in any healthy lymphoid tissue examined. Lymphoid cell lines overexpressing MCT-1 exhibited increased growth rates and displayed increased protection against apoptosis induced by serum starvation when compared with matched controls. We found that MCT-1-overexpressing cells show constitutively higher levels of phosphorylated PKB/Akt protein, especially under serum starvation. Activation of survival pathways may be an additional function of the MCT-1 gene. Our data suggest that high levels of MCT-1 protein may be associated with a high-risk subset of lymphoid neoplasms and may further support the potential role of MCT-1 in promoting human lymphoid tumor development.

Interleukin 4-induced gene 1 is activated in primary mediastinal large B-cell lymphoma

The molecular markers that distinguish primary mediastinal large B-cell lymphoma (PMBL) from nonmediastinal diffuse large B-cell lymphomas (NM-DLBLs) remain to be identified. Using cDNA representational difference analysis to compare PMBL and NM-DLBL transcripts, we isolated a cDNA fragment homologous to the mouse B-cell interleukin 4 (IL-4)-inducible gene FIG1 (interleukin 4-induced gene 1) transcript. The human FIG1 mRNA encodes a 567 amino acid protein that comprises a signal peptide and a large flavin-binding amino oxidase domain, and shares significant homology with secreted apoptosis-inducing L-amino acid oxidases. Northern blot studies showed that FIG1 mRNA expression is mainly restricted to lymphoid tissues. It is expressed at low levels in thymus, spleen, tonsils, and reactive lymph nodes, and is highly up-regulated in IL-4+CD40-activated tonsillar B cells. Interestingly, in human B-cell lines, FIG1 mRNA expression appeared restricted to the PMBL-derived MedB-1 and Karpas 1106 cell lines. Using real-time reverse transcriptase-polymerase chain reaction (RT-PCR), we demonstrated that all but one PMBL (16/17) displayed high FIG1 mRNA levels, whereas most NM-DLBLs (12/18) and all low-grade B-cell lymphomas tested (8/8) exhibited low FIG1 mRNA levels. The difference between PMBLs and NM-DLBLs was statistically significant (Fisher test; P =.0003). Southern blot studies did not show rearrangement of the FIG1 gene. FIG1 gene expression might be due to a constitutive activation of a cytokine signaling pathway in PMBL.

Compilation of published comparative genomic hybridization studies

The power of comparative genomic hybridization (CGH) has been clearly proven since the first paper appeared in 1992 as a tool to characterize chromosomal imbalances in neoplasias. This review summarizes the chromosomal imbalances detected by CGH in solid tumors and in hemopathies. In May of 2001, we took a census of 430 articles providing information on 11,984 cases of human solid tumors or hematologic malignancies. Comparative generic hybridization has detected a number of recurrent regions of amplification or deletion that allows for identification of new chromosomal loci (oncogenes, tumor suppressor genes, or other genes) involved in the development, progression, and clonal evolution of tumors. When CGH data from different studies are combined, a pattern of nonrandom genetic aberrations appears. As expected, some of these gains and losses are common to different types of pathologies, while others are more tumor-specific.

Mediastinal (thymic) large B-cell lymphoma: where do we stand?

Mediastinal (thymic) B-cell lymphoma (MBL) is a locally highly aggressive tumour that was first definitively described in the early 1980s. The incidence of MBL is low, which made disease characterisation difficult initially. However, MBL has several peculiar clinical, morphological, immunological, and genetic features. Collectively, these characteristics distinguish it from other diffuse, large B-cell lymphomas. Consequently, MBL has become a defined subtype of diffuse large B-cell lymphoma with its own code (9679/3) in the International Classification of Diseases. New insights into the biological and clinical aspects of MBL have been gained from the study of large numbers of cases. Nevertheless, the histogenesis of the disease is not yet fully understood. We review the available data on MBL with special emphasis on its morphological, immunological, and genetic properties. Also discussed are recent data on molecular genetics, biology, and treatment.

Expression and stabilization of the MCT-1 protein by DNA damaging agents

The contribution of oncogene amplification and/or overexpression to T-cell lymphoid neoplasms has only of late been established with the implication of the TCL1 and MTCP1 genes in T-cell malignancies. Our laboratory has recently discovered a novel oncogene, MCT-1, amplified in a T-cell lymphoma and mapped to chromosome Xq22-24. MCT-1 has been shown to decrease cell-doubling time, dramatically shortening the duration of G(1) transit time and/or G1-S transition, and transforms NIH3T3 fibroblasts. Constitutive expression of MCT-1 results in a strong proliferative signal and is associated with deregulation of protein kinase-mediated G1/S phase checkpoints. In this study we analysed the level and subcellular localization of this novel cell cycle regulatory molecule as a function of cell cycle phase. In human lymphoid tumors expression of MCT-1 is constant throughout the cell cycle and remains cytoplasmic. Cells overexpressing MCT-1 have increased expression of cyclin D1 with dysregulation of the G(1)-S checkpoint. Both cyclin D1 and MCT-1 are involved in regulating passage of cells through the G1 phase of the cell cycle. Since prior work has shown that gamma irradiation induces cyclin D1 expression we investigated the induction of MCT-1 to DNA damaging agents. We demonstrate that increases in MCT-1 protein in irradiated human lymphoid cells do not occur at the mRNA level and do not require new protein synthesis.

Alteration of chromosome arm 6p is characteristic of primary mediastinal B-cell lymphoma, as identified by genome-wide allelotyping

Five cases of primary mediastinal B-cell lymphoma (PMBL) each have been studied with 375 microsatellite markers from all 22 autosomes. Of the 151 genomic alterations among the 1,875 assays, only five were allelic losses. The remainder of the microsatellite alterations consisted of 114 allelic imbalances and 32 instabilities. Microsatellite alterations were found in all cases on chromosomal arms 6p and 9p. These allelic imbalances most likely are indicative of genetic amplification, a finding agreeing well with those of studies using either comparative genomic hybridization or arbitrarily primed polymerase chain reaction, in which amplification of chromosome arm 9p in PMBL has been found. The allelic imbalances on chromosome arm 6p always included marker D6S276 located at 6p21.3-p22.3, where the MHC class I genes reside. These allelic imbalances may be reflective of alterations in the expression of the MHC gene products, characteristic of PMBL. Allelic anomalies close to the MYB gene locus on 6q were detected in two cases and prompted the analysis of MYB rearrangements in a series of 30 lymphomas. One rearrangement was detected in one of 18 cases of PMBL and in none of 10 diffuse, large B-cell lymphomas and two T-cell lymphomas. Our genome-wide microsatellite analysis provides independent confirmation that PMBL is characterized by infrequent chromosomal losses and by frequent genetic alterations involving chromosomal arm 9p. For the first time, chromosomal arm 6p has been identified as a highly frequent target of genetic alterations in this tumor type. Finally, MYB may also be involved occasionally in PMBL pathogenesis.

MedB-1, a human tumor cell line derived from a primary mediastinal large B-cell lymphoma

Primary mediastinal B-cell lymphoma is a locally highly aggressive but poorly disseminating tumor composed of medium sized or large cells most probably of thymic medullary origin. It has a mature B-cell phenotype, typically lacks immunoglobulin expression and has variable defects in expression of HLA-molecules. We present here a cell line, MedB-1, derived from such a tumor. As is frequently found in mediastinal B-cell lymphomas in situ, MedB-1 is CD10(-), CD19(+), CD21(-), CD22(+), CD23(+), CD25(-), CD37(+), CD38(-), CD39(+), CD40(+), CD54(+), CD95(+). Like the parental tumor, MedB-1 lacks HLA-A,B,C alpha-chains and beta(2)microglobulin and expresses HLA-D molecules at decreased levels. Both parental tumor and MedB-1 cells are clonally related as shown by immunoglobulin heavy chain gene rearrangement analysis. Unlike the parental tumor tissue, the MedB-1 cell line cytoplasmically expresses IgG/kappa in a very small subset of cells under standard culture conditions. MedB-1 does not contain any Epstein-Barr virus DNA. In a tissue adhesion assay MedB-1 cells showed an extensive binding to the medullary region of normal thymus. Altogether, MedB-1 is a suitable tool for functional and molecular analysis of this distinct lymphoma entity.

Gain of chromosome arm 9p is characteristic of primary mediastinal B-cell lymphoma (MBL): comprehensive molecular cytogenetic analysis and presentation of a novel MBL cell line

Primary mediastinal B-cell lymphoma (MBL) is an aggressive Non-Hodgkin's Lymphoma, which has been recognized as a distinct disease entity. We performed a comprehensive molecular cytogenetic study analyzing 43 MBLs. By comparative genomic hybridization (CGH), the most common aberrations were gains of chromosome arms 9p and Xq, which were present in 56% and 40% of cases, respectively. Based on the limited resolution of CGH, this technique may underestimate the real incidence of aberrations. Therefore, we also did an interphase cytogenetic study with eight DNA probes mapping to chromosome regions frequently altered in B-cell lymphomas. With this approach, both 9p and Xq gains were found in more than 70% of cases (75% and 87%, respectively). The findings were compared with results obtained in 308 other B-cell lymphomas. Gains in 9p were identified in only six of the 308 cases, and only one of these lymphomas with 9p gains was not primarily extranodal in origin (P < 10-(20) for CGH data and P < 10-(11) for fluorescence in situ hybridization data). We also present a novel MBL cell line, MedB-1, which carries the genetic aberrations characteristic of this entity.

Genetic alterations in primary mediastinal B-cell lymphoma: an update

Primary mediastinal B-cell lymphoma (PMBL) is a distinct clinical entity among non-Hodgkin's lymphoma. The malignancy has received little attention from a standpoint of basic research due in part to its rarity. However, based on recent studies consistent trends are beginning to emerge regarding the molecular and chromosomal alterations commonly observed in this disease. By both CGH and AP-PCR, genetic gains involving chromosomes 2, 5, 7, 9p, 12, and Xq are among the most frequently observed events. From a molecular standpoint, alterations in the c-myc, p16(INK4) and p53 genes have been observed in up to 30% of cases. This information along with the well-established histological, immunological, and clinical features should convince the few remaining disbelievers that PMBL is a distinct pathological entity among non-Hodgkin's lymphomas.

Comparative genomic hybridization: uses and limitations

Comparative genomic hybridization (CGH) has contributed significantly to the current knowledge of genomic alterations in hematologic malignancies. Characteristic patterns of genomic imbalances not only have confirmed recent classification schemes in non-Hodgkin's lymphoma, but they provide a basis for the successful identification of genes with previously unrecognized pathogenic roles in the development of different lymphomas. Based on its technical limitations, there is little reason to apply CGH to chromosomes of metaphase cells in routine diagnostic settings. However, the new approach of CGH to DNA microarrays, a procedure termed matrix-CGH, overcomes most of the limitations and opens new approaches for diagnostics and identification of genetically defined leukemia and lymphoma subgroups. Current efforts to develop leukemia specific matrix-CGH DNA chips, which are designed to meet the clinical needs, are presented and discussed.

Pancreatic acinar carcinoma shows a distinct pattern of chromosomal imbalances by comparative genomic hybridization

Pancreatic acinar cell carcinoma (PAC) is a rare pancreatic tumor for which no information about chromosomal anomalies is available. We examined six primary PACs by comparative genomic hybridization (CGH). All cases showed chromosomal changes. A total of 106 gains and 48 losses was detected. Consensus regions of gain were identified on chromosomes 1, 12, and X: 1q21 in four cases, 1q42 in three cases, 12p11.2 in four cases, and Xq12-21 in three cases. Recurrent losses were found at 16p13.2-p13.1 in three cases and at 16q23 in three cases. To verify these chromosomal imbalances, microsatellite analysis of matched normal and tumor DNA was performed using PCR-amplified markers for chromosomes 1, 12, and 16 in the regions showing nonrandom gains or losses. This analysis showed allelic imbalances in tumor DNA consistent with the CGH profiles. Our CGH study suggests that PAC shows a characteristic pattern of chromosomal alterations, involving gain at 1q, 12p, and Xq and loss of sequences at 16p and 16q. This pattern appears unique among solid tumors and is markedly different from that detected in pancreatic ductal carcinomas by the same technique. This suggests that PAC tumorigenesis involves different molecular pathways than those involved in the more common pancreatic ductal tumors. Genes Chromosomes Cancer 28:294-299, 2000.

Molecular features of primary mediastinal B-cell lymphoma: involvement of p16INK4A, p53 and c-myc

Primary mediastinal B-cell lymphoma (PMBL) shows chromosome 9p anomalies in 50% of cases. Based on reports that p16INK4A gene, located on this chromosomal arm, is frequently altered in aggressive lymphomas, we analysed for alterations of this gene in 27 cases of PMBL, which were part of a series of 32 PMBL cases that have been characterized for alterations in c-myc, p53, N-ras, bcl-1, bcl-2, bcl-6 and for Epstein-Barr virus (EBV) infection. Four cases showed p16INK4A gene anomalies, including three with promoter methylation and one homozygous deletion. Eight PMBLs showed c-myc rearrangements. Three additional cases showed sequence variations in the c-myc P2 promoter, two of which consisted of the same germline variation involving a novel polymorphic XhoI site. Four tumours contained p53 gene mutations and three had clonal EBV infection. One case had a bcl-6 rearrangement. In conclusion, our study shows that p16INK4, c-myc and p53 alterations occur in 15%, 25% and 13% of PMBLs, respectively. EBV monoclonality was found in 9% of cases, whereas no abnormality was detected in bcl-1, bcl-2 and N-ras. Thus, none of the common genetic aberrations seen in other types of non-Hodgkin's lymphomas appears to be stringently involved in the pathogenesis of this unique lymphoma type.