New chromosomal alterations in a series of 23 splenic marginal zone lymphoma patients revealed by Spectral Karyotyping (SKY)

Clinical and biological features of B-cell neoplasms with CDK6 translocations: an association with a subgroup of splenic marginal zone lymphomas displaying frequent CD5 expression, prolymphocytic cells, and TP53 abnormalities

A translocation involving the cyclin-dependent kinase 6 (CDK6) gene [t(CDK6)] is a rare but recurrent abnormality in B-cell neoplasms. To further characterise this aberration, we studied 57 cases; the largest series reported to date. Fluorescence in situ hybridisation analysis confirmed the involvement of CDK6 in all cases, including t(2;7)(p11;q21) immunoglobulin kappa locus (IGK)/CDK6 (n = 51), t(7;14)(q21;q32) CDK6/immunoglobulin heavy locus (IGH) (n = 2) and the previously undescribed t(7;14)(q21;q11) CDK6/T-cell receptor alpha locus (TRA)/T-cell receptor delta locus (TRD) (n = 4). In total, 10 patients were diagnosed with chronic lymphocytic leukaemia, monoclonal B-cell lymphocytosis or small lymphocytic lymphoma, and 47 had small B-cell lymphoma (SmBL) including 36 cases of marginal zone lymphoma (MZL; 34 splenic MZLs, one nodal MZL and one bronchus-associated lymphoid tissue lymphoma). In all, 18 of the 26 cytologically reviewed cases of MZL (69%) had an atypical aspect with prolymphocytic cells. Among the 47 patients with MZL/SmBL, CD5 expression was found in 26 (55%) and the tumour protein p53 (TP53) deletion in 22 (47%). The TP53 gene was mutated in 10/30 (33%); the 7q deletion was detected in only one case, and no Notch receptor 2 (NOTCH2) mutations were found. Immunoglobulin heavy-chain variable-region (IGHV) locus sequencing revealed that none harboured an IGHV1-02*04 gene. Overall survival was 82% at 10 years and not influenced by TP53 aberration. Our present findings suggest that most t(CDK6)+ neoplasms correspond to a particular subgroup of indolent marginal zone B-cell lymphomas with distinctive features.

Deciphering splenic marginal zone lymphoma pathogenesis: the proposed role of microRNA

Splenic marginal zone lymphoma (SMZL) is a malignancy of mature B-cells that primarily involves the spleen, but can affect peripheral organs as well. Even though SMZL is overall considered an indolent malignancy, the majority of cases will eventually progress to be more aggressive. In recent years, the gene expression profile of SMZL has been characterized in an effort to identify: 1) the etiology of SMZL, 2) biological consequences of SMZL, and 3) putative therapeutic targets. However, due to the vast heterogeneity of the malignancy, no conclusive target(s) have been deciphered. However, the role of miRNA in SMZL, much as it has in chronic lymphocytic leukemia, may serve as a guiding light. As a result, we review the comprehensive expression profiling in SMZL to-date, as well as describe the miRNA (and potential mechanistic roles) that may play a role in SMZL transformation, particularly within the 7q region.

Translocation t(2;7)(p11;q21) associated with the CDK6/IGK rearrangement is a rare but recurrent abnormality in B-cell lymphoproliferative malignancies

Structural abnormalities of chromosome 7q have been regularly reported in chronic B-cell lymphoproliferative disorders. They include chromosomal translocations involving 7q21, leading to overexpression of the CDK6 gene. Three different translocations, t(7;14)(q21;q32), t(7;22)(q21;q11), and t(2;7)(p11;q21), leading to the juxtaposition of the CDK6 gene with a immunoglobulin gene enhancer during B-cell differentiation, have been described. In the past 2 years, we identified three patients with lymphoproliferative malignancy associated with a t(2;7)(p11;q21). Fluorescent in situ hybridization using an IGK probe and a library of bacterial artificial chromosome (BAC) clones located in bands 7q21.2 and 7q21.3, containing CDK6, revealed that the telomeric part of the IGK probe was translocated on the der(7) within a 51-kb region upstream of the transcriptional start site of CDK6. A total of 23 patients with indolent B-cell lymphoproliferative disorders and juxtaposition of the IG and CDK6 genes, including 20 with IGK and CDK6 juxtaposition, have been reported thus far. This rearrangement leads to the overexpression of CDK6, which encodes a cyclin-dependent protein kinase involved in cell cycle G1 phase progression and G1/S transition.

Splenic marginal zone lymphoma: comprehensive analysis of gene expression and miRNA profiling

Splenic marginal zone lymphoma is a small B-cell neoplasm whose molecular pathogenesis is still essentially unknown and whose differentiation from other small B-cell lymphomas is hampered by the lack of specific markers. We have analyzed the gene expression and miRNA profiles of 31 splenic marginal zone lymphoma cases. For comparison, 7 spleens with reactive lymphoid hyperplasia, 10 spleens infiltrated by chronic lymphocytic leukemia, 12 spleens with follicular lymphoma, 6 spleens infiltrated by mantle cell lymphoma and 15 lymph nodes infiltrated by nodal marginal zone lymphoma were included. The results were validated by qRT-PCR in an independent series including 77 paraffin-embedded splenic marginal zone lymphomas. The splenic marginal zone lymphoma miRNA signature had deregulated expression of 51 miRNAs. The most highly overexpressed miRNAs were miR-155, miR-21, miR-34a, miR-193b and miR-100, while the most repressed miRNAs were miR-377, miR-27b, miR-145, miR-376a and miR-424. MiRNAs located in 14q32-31 were underexpressed in splenic marginal zone lymphoma compared with reactive lymphoid tissues and other B-cell lymphomas. Finally, the gene expression data were integrated with the miRNA profile to identify functional relationships between genes and deregulated miRNAs. Our study reveals miRNAs that are deregulated in splenic marginal zone lymphoma and identifies new candidate diagnostic molecules for splenic marginal zone lymphoma.

Next-generation sequencing discoveries in lymphoma

Since the mapping of the human genome and the advent of next-generation sequencing technology thorough examination of the cancer genome has become a reality. Over the last few years several studies have used next-generation sequencing technology to investigate the genetic landscape of Hodgkin and non-Hodgkin lymphomas, identifying novel genetic mutations and gene rearrangements that have shed new light on the underlying tumor biology in these diseases as well as identifying possible targets for directed therapy. This review covers the major discoveries in lymphoma using next-generation sequencing technology.

Sequencing of t(2;7) translocations reveals a consistent breakpoint linking CDK6 to the IGK locus in indolent B-cell neoplasia

The translocation t(2;7)(p11;q21) has repeatedly been documented in association with indolent B-cell lymphoproliferative disorders (BLPDs). However, the chromosomal breakpoints associated with this recurrent translocation have rarely been characterized. Using an approach based on long-range PCR, we mapped the t(2;7) breakpoints in five patients presenting with indolent B-cell neoplasia. The sequencing of these rearrangements revealed several striking parallels across the t(2;7) breakpoints. The junction sites on 2p11 consistently mapped to the heptamer recombination signal sequence (RSS) of an immunoglobulin kappa variable gene (IGK) within the Vκ3 family, while the breakpoints on 7q21 each localized to within 4 bp of an RSS-like element located approximately 0.5 kb upstream of the transcription start site of the cyclin-dependent kinase 6 gene (CDK6). These findings confirm the significant genetic overlap arising in BLPD-associated t(2;7) translocations, and implicate the deregulated expression of CDK6 as a common molecular mechanism involved in the emergence of clonal B-cell proliferations presenting with this recurrent abnormality. In addition, the successful mapping of the t(2;7) translocations in each of five patients using a simple PCR-based protocol highlights the potential diagnostic utility of this approach during characterization of cases harboring analogous rearrangements.

Molecular characterization of a t(2;7) translocation linking CDK6 to the IGK locus in CD5(-) monoclonal B-cell lymphocytosis

The term monoclonal B-cell lymphocytosis (MBL) is used to characterize individuals with a circulating population of clonal B-cells and no other features of a lymphoproliferative disorder. Although several recent studies have examined the molecular basis of this condition, the subgroup of MBL lacking CD5 expression has been largely overlooked. In this study, we sequenced a t(2;7) in a patient with persistent but non-progressing CD5(-) MBL. This revealed a breakpoint at 2p11.2 localized to the recombination signal sequence (RSS) of the immunoglobulin κ (IGK) variable gene IGKV3-15, and a breakpoint at 7q21.2 located 520 base pairs (bp) upstream of the transcription start site of cyclin-dependent kinase 6 (CDK6 ). The 7q breakpoint showed perfect sequence homology to the immunoglobulin RSS heptamer, and was located within 3 bp of a t(2;7) junction previously characterized in splenic marginal zone lymphoma (SMZL). These findings highlight a genetic link between CD5(-) MBL and SMZL, and implicate the dysregulation of CDK6 in the emergence of this preclinical disorder.

Cytogenetic aberrations and their prognostic value in a series of 330 splenic marginal zone B-cell lymphomas: a multicenter study of the Splenic B-Cell Lymphoma Group

We conducted a retrospective collaborative study to cytogenetically characterize splenic marginal zone lymphoma (SMZL) and ascertain the prognostic value of chromosomal aberrations. Of 330 cases, 72% displayed an aberrant karyotype, 53% were complex, and 29% had a single aberration. The predominant aberrations were gains of 3/3q and 12q, deletions of 7q and 6q and translocations involving 8q/1q/14q. CD5 expression was detected in 39 of 158 cases (25%). The cytogenetic makeup of the CD5+ group differed significantly from that of the CD5− group. Cases with unmutated IGHV were significantly associated with deletions of 7q and TP53. A strong association was noted between usage of the IGVH1-2 and deletion 7q, 14q alterations, and abnormal karyotype. On univariate analysis, patients with more than or equal to 2 aberrations, 14q alterations, and TP53 deletions had the shortest survival; 7q deletion did not affect survival. On multivariate analysis, cytogenetic aberrations did not retain prognostic significance; the parameters negatively affecting survival were hemoglobin and age. In conclusion, the cytogenetic profile of SMZL is distinct from other B-cell lymphomas. Complexity of the karyotype, 14q aberrations, and TP53 deletions are poor prognostic indicators and may be considered together with other clinicobiologic parameters to ascertain the prognosis of SMZL.

CD5 expression identifies a subset of splenic marginal zone lymphomas with higher lymphocytosis: a clinico-pathological, cytogenetic and molecular study of 24 cases

BACKGROUND

Classically, splenic marginal zone B-cell lymphoma is characterized by the absence of CD5 expression. Cases of apparent splenic marginal zone B-cell lymphoma showing CD5 expression, as diagnosed by blood studies, have been described; however, in the absence of histological evidence, the correct diagnosis of these cases is controversial because of possible confusion with other CD5-positive small B-cell neoplasms.

DESIGN AND METHODS

We report a series of 24 CD5-positive, t(11;14)-negative cases of splenic marginal zone B-cell lymphoma diagnosed by flow cytometry studies of blood and histologically proven on spleen sections. Clinical data as well as morphological, immunological, cytogenetic and molecular characteristics were assessed to evaluate the similarities and differences of these cases with those of classical CD5-negative splenic marginal zone B-cell lymphoma.

RESULTS

The CD5 expression detected in blood by flow cytometry was confirmed in most cases by immunohistochemistry on spleen sections. In general, cases of CD5-positive and CD5-negative splenic marginal zone B-cell lymphoma did not appear different and, in particular, they showed similar karyotypic changes such as 7q deletion, trisomy 3, trisomy 18 and biased IGHV usage (i.e. VH1-2). The main differences were a higher lymphocyte count at diagnosis (8.15x10(9)/L versus 3.90x10(9)/L; P=0.005) and more frequent diffuse bone marrow infiltration (34% versus 8%; P=0.03) in the CD5-positive group. A tendency to a more mutated IGHV status in the CD5 positive cases was observed (80% versus 54.5%; (P=0.11). No significant differences in outcome were found in relation to CD5 expression.

CONCLUSIONS

This study confirms the existence of cases of CD5-positive splenic marginal zone B-cell lymphoma and shows that these cases are closely related to classical splenic marginal zone lymphoma. Whether or not CD5-positive splenic marginal zone B-cell lymphoma constitutes a true subset obviously requires the study of more cases.

High-resolution genome-wide array comparative genomic hybridization in splenic marginal zone B-cell lymphoma

Splenic marginal zone B-cell lymphoma is characterized by high genetic heterogeneity, and hepatitis C virus infection seems to be involved in a subset of patients. The aims of the analysis were to identify potential genetic alterations related to hepatitis C virus status, IgV(H) gene mutational status, and prognostic categories identified in a multicenter study (Blood 2006;107:4643). Genome-wide array comparative genomic hybridization at a 100-kilobase (kb) resolution was performed in 34 patients with splenic marginal zone B-cell lymphoma, 12 of whom were hepatitis C virus positive. Array-comparative genomic hybridization experiments revealed no copy number alterations in 10 patients (4 were hepatitis C virus positive). A median of 5.6 and 3.8 copy number alterations were detected in hepatitis C virus-positive and in hepatitis C virus-negative patients, respectively. The most frequent copy number alterations involved chromosomes 7 and 17 (21% and 24%, respectively). Except for Xp gain (P = .01), no differences in common alterations were found between hepatitis C virus-positive and hepatitis C virus-negative cases. Unmutated status of the IgV(H) gene was related to del(7q) (P = .04) and dup(12q) (P = .03). The high-risk group identified according to the new splenic marginal zone B-cell lymphoma prognostic score was associated with del(7q) (P = .01) and del(17p) (P = .02). Hepatitis C virus-positive splenic marginal zone B-cell lymphoma patients have no specific chromosome alterations. Patients with poor prognosis are characterized by distinctive imbalances.

Multiple recurrent chromosomal breakpoints in mantle cell lymphoma revealed by a combination of molecular cytogenetic techniques

Mantle cell lymphoma (MCL) is genetically characterized by 11q13 translocations leading to the overexpression of CCND1, and additional secondary genomic alterations that may be important in the progression of this disease. We have analyzed 22 MCL cases and 10 MCL cell lines using multicolor fluorescence in situ hybridization (M-FISH), FISH, and comparative genomic hybridization (CGH). The 19 cases with abnormal karyotype showed the t(11;14)(q13;q32) translocation and, additionally, 89% of cases showed both numerical (n = 58) and structural (n = 77) aberrations. All but one MCL cell line showed t(11;14) and structural and numerical alterations in highly complex karyotypes. Besides 11 and 14, the most commonly rearranged chromosomes were 1, 8, and 10 in the tumors and 1, 8, and 9 in the cell lines. No recurrent translocations other than the t(11;14) were identified. However, we identified 17 recurrent breakpoints, the most frequent being 1p22 and 8p11, each observed in four cases and two cell lines. Interestingly, five tumors and four cell lines displayed a complex t(11;14), cryptic in one case and two cell lines, preferentially involving chromosome 8. In typical MCL, ATM gene deletions were significantly associated with a high number of structural and numerical alterations. In conclusion, MCL does not have recurrent translocations other than t(11;14), but shows recurrent chromosomal breakpoints. Furthermore, most MCL harbor complex karyotypes with a high number of both structural and numerical alterations affecting several common breakpoints, leading to various balanced and unbalanced translocations.