The t(9;14)(p13;q32) translocation in B-cell non-Hodgkin's lymphoma

The PAX Genes: Roles in Development, Cancer, and Other Diseases

Since their 1986 discovery in Drosophila, Paired box (PAX) genes have been shown to play major roles in the early development of the eye, muscle, skeleton, kidney, and other organs. Consistent with their roles as master regulators of tissue formation, the PAX family members are evolutionarily conserved, regulate large transcriptional networks, and in turn can be regulated by a variety of mechanisms. Losses or mutations in these genes can result in developmental disorders or cancers. The precise mechanisms by which PAX genes control disease pathogenesis are well understood in some cases, but much remains to be explored. A deeper understanding of the biology of these genes, therefore, has the potential to aid in the improvement of disease diagnosis and the development of new treatments.

CD5-Negative, CD10-Negative Low-Grade B-Cell Lymphoproliferative Disorders of the Spleen

CD5-negative, CD10-negative low-grade B-cell lymphoproliferative disorders (CD5-CD10-LPD) of the spleen comprise a fascinating group of indolent, neoplastic, mature B-cell proliferations that are essential to accurately identify but can be difficult to diagnose. They comprise the majority of B-cell LPDs primary to the spleen, commonly presenting with splenomegaly and co-involvement of peripheral blood and bone marrow, but with little to no involvement of lymph nodes. Splenic marginal zone lymphoma is one of the prototypical, best studied, and most frequently encountered CD5-CD10-LPD of the spleen and typically involves white pulp. In contrast, hairy cell leukemia, another well-studied CD5-CD10-LPD of the spleen, involves red pulp, as do the two less common entities comprising so-called splenic B-cell lymphoma/leukemia unclassifiable: splenic diffuse red pulp small B-cell lymphoma and hairy cell leukemia variant. Although not always encountered in the spleen, lymphoplasmacytic lymphoma, a B-cell lymphoproliferative disorder consisting of a dual population of both clonal B-cells and plasma cells and the frequent presence of the MYD88 L265P mutation, is another CD5-CD10-LPD that can be seen in the spleen. Distinction of these different entities is possible through careful evaluation of morphologic, immunophenotypic, cytogenetic, and molecular features, as well as peripheral blood and bone marrow specimens. A firm understanding of this group of low-grade B-cell lymphoproliferative disorders is necessary for accurate diagnosis leading to optimal patient management.

Diffuse large B-cell lymphoma carrying t(9;14)(p13;q32)/PAX5-immunoglobulin heavy chain gene is characterized by nuclear positivity of MUM1 and PAX5 by immunohistochemistry

We described four patients with diffuse large B-cell lymphoma (DLBCL) carrying t(9;14)(p13;q32) that places the PAX5 adjacent to the immunoglobulin heavy chain (IGH) gene. Ages ranged between 63 and 80, and three were female. One developed a nodal disease, and the other three involved extranodal organs. The lymphoma cells were CD10^- /BCL6^- /MUM1⁺ in three and CD10⁺ /BCL6⁺ /MUM1⁺ in one. BCL2 was weak or negative. All had t(9;14)(p13;q32), and three had additional 14q32/IGH translocations or +der(14)t(9;14)(p13;q32). Fluorescence in situ hybridization using the PAX5 break-apart probe showed that the locus was disrupted between the 5' and 3' probes or within the 5' probe. Immunohistochemistry (IHC) using a monoclonal antibody against PAX5 showed strong nuclear positivity in all four patients. Cell block IHC of a CD30⁺ DLBCL cell line, KIS-1, which carried the t(9;14)(p13;q32) and PAX5-IGH fusion gene, reproduced the CD10^- /BCL6^- /MUM1⁺ immunophenotype, low-level BCL2, and strong nuclear PAX5. Uniform nuclear positivity of MUM1 in all four cases and KIS-1 cells suggest that these lymphomas arose at a late stage of B-cell differentiation, where expression of PAX5 physiologically becomes downregulated. It is therefore possible that high-level PAX5 resulting from t(9;14)(p13;q32) at this stage of differentiation perturbs the plasma cell differentiation program initiated by PAX5 repression, thereby contributing to the development of a fraction of DLBCL.

Immunoglobulin gene translocations in chronic lymphocytic leukemia: A report of 35 patients and review of the literature

Chronic lymphocytic leukemia (CLL) represents the most common hematological malignancy in Western countries, with a highly heterogeneous clinical course and prognosis. Translocations involving the immunoglobulin (IG) genes are regularly identified. From 2000 to 2014, we identified an IG gene translocation in 18 of the 396 patients investigated at diagnosis (4.6%) and in 17 of the 275 analyzed during follow-up (6.2%). A total of 4 patients in whom the IG translocation was identified at follow-up did not carry the translocation at diagnosis. The IG heavy locus (IGH) was involved in 27 translocations (77.1%), the IG κ locus (IGK) in 1 (2.9%) and the IG λ locus (IGL) in 7 (20.0%). The chromosome band partners of the IG translocations were 18q21 in 16 cases (45.7%), 11q13 and 19q13 in 4 cases each (11.4% each), 8q24 in 3 cases (8.6%), 7q21 in 2 cases (5.7%), whereas 6 other bands were involved once (2.9% each). At present, 35 partner chromosomal bands have been described, but the partner gene has solely been identified in 10 translocations. CLL associated with IG gene translocations is characterized by atypical cell morphology, including plasmacytoid characteristics, and the propensity of being enriched in prolymphocytes. The IG heavy chain variable region (IGHV) mutational status varies between translocations, those with unmutated IGHV presumably involving cells at an earlier stage of B-cell lineage. All the partner genes thus far identified are involved in the control of cell proliferation and/or apoptosis. The translocated partner gene becomes transcriptionally deregulated as a consequence of its transposition into the IG locus. With the exception of t(14;18)(q32;q21) and its variants, prognosis appears to be poor for the other translocations. Therefore, searching for translocations involving not only IGH, but also IGL and IGK, by banding and molecular cytogenetics is required. Furthermore, it is important to identify the partner gene to ensure the patients receive the optimal treatment.

PAX5 is expressed in small-cell lung cancer and positively regulates c-Met transcription

PAX5 is a nuclear transcription factor required for B cell development, and its expression was evaluated in upper aerodigestive malignancies and pancreatic cancer by immunoblotting. The PAX5 protein expression was relatively strong in small-cell lung cancer (SCLC, 11/12); however, its expression was not detected in non-SCLC (NSCLC, n=13), mesothelioma (n=7), pancreatic (n=6), esophageal (n=6) and head and neck cancer cell lines (n=12). In comparison, PAX8 and PAX3 expressions were absent or non-detectable in SCLC cell lines; however, PAX8 was expressed in most of the tested NSCLC cell lines (13/13) and also frequently in all the other cell lines. We also detected frequent expressions of PAX2 and PAX9 protein in the various cell lines. Utilizing neuroendocrine tumor samples, we found that the frequency as well as the average intensity of the expression of PAX5 increased from pulmonary carcinoid (9%, moderate and strong PAX5 expression, n=44), to large-cell neuroendocrine carcinoma (LCNC, 27%, n=11) to SCLC (33%, n=76). FISH analysis revealed no translocations of the PAX5 gene, but polyploidy in some SCLC tumor tissues (6/37). We determined that PAX5 could regulate the transcription of c-Met using luciferase-coupled reporter and chromatin immunoprecipitation analysis. In addition, the phospho-c-Met (active form) and PAX5 were both localized to the same intra-nuclear compartment in hepatocyte growth factor treated SCLC cells and interacted with each other. Finally, we determined the therapeutic translational potential of PAX5 using PAX5 knockdown SCLC cells in conjunction with Topoisomerase 1 (SN38) and c-Met (SU11274) inhibitors. Loss of endogenous PAX5 significantly decreased the viability of SCLC cells, especially when combined with SN38 or SU11274, and maximum effect was seen when both inhibitors were used. Therefore, we propose that PAX5 could be an important regulator of c-Met transcription and a potential target for therapy in SCLC.

Waldenström macroglobulinaemia

Over time, Waldenström macroglobulinaemia (WM) has evolved conceptually from a clinical syndrome to a distinct clinicopathological entity. Progress is being made in standardization of the disease definition and treatment response criteria, although nosologic controversies persist. According to the Second International Workshop on WM, the disease is defined as a B-cell neoplasm characterized by a lymphoplasmacytic infiltrate in the bone marrow, with an associated immunoglobulin (Ig) M paraprotein. Disease symptoms are often divided into those related to tumour infiltration and those related to the rheological effects of the monoclonal IgM. As with other low-grade lymphomas, asymptomatic patients are observed only, with treatment reserved for symptomatic patients. There is no standard treatment for WM and choices include rituximab, alkylating agents, purine nucleoside analogues, alone or in combination, as well as autologous peripheral blood stem cell transplant in eligible patients. Novel treatments, such as bortezomib, oblimersen sodium, perifosine and others are being evaluated.

Genomics and proteomics in multiple myeloma and Waldenström macroglobulinemia

PURPOSE OF REVIEW

Multiple myeloma and Waldenström macroglobulinemia are incurable hematologic malignancies with similar clinical phenotypes characterized by over-production of monoclonal immunoglobulins. Translocations into the immunoglobulin heavy chain locus and aneuploidy are nearly universal in multiple myeloma, whereas Waldenström macroglobulinemia generally does not harbor translocations. Deletion of 6q is identified in 50% of patients with Waldenström macroglobulinemia, however. The genetic abnormalities in multiple myeloma and Waldenström macroglobulinemia have implications for disease progression, and the subsequent proteomic expression associated with each disease influences therapeutic decisions.

RECENT FINDINGS

Gene expression profiling in these hematologic malignancies demonstrated distinct differences in mRNA expression patterns. Following profiling, Waldenström macroglobulinemia samples clustered with chronic lymphocytic leukemia and normal B-cell samples. Profiling performed after separation of Waldenström macroglobulinemia samples into populations with plasma cell or B-cell morphology revealed that plasma cell Waldenström macroglobulinemia samples most closely resembled multiple myeloma samples rather than chronic lymphocytic leukemia or normal control samples.

SUMMARY

Diverse genetic abnormalities have been identified in these hematologic malignancies, although they have similar clinical features. Gene expression profiling has elucidated the impact of genetic abnormalities. Furthermore, it may be used to identify a specific pathway for therapeutic targeting, such as interleukin-6 in Waldenström macroglobulinemia.

Comparative genome-wide profiling of post-transplant lymphoproliferative disorders and diffuse large B-cell lymphomas

Post-transplant lymphoproliferative disorders (PTLD) are a major complication of solid organ transplantation, representing a cause of severe morbidity and mortality. Apart from Epstein-Barr virus infection, knowledge of the pathogenesis of monoclonal PTLD is limited. Powerful analysis techniques, such as whole genomic DNA profiling (array comparative genomic hybridisation), can improve our understanding of PTLD pathogenesis. Whole genome profiling using the Affymetrix GeneChip Human Mapping 10 k 2.0 was performed on 20 PTLD cases and 25 cases of diffuse large B-cell lymphoma (DLBCL) from immunocompetent patients as a control group. Recurrent lesions were detected among all the samples. Chromosome 18q, 7q, 3q and 12 were the most common gains in the control group. Chromosomes 5p and 11p were commonly gained in PTLD-DLBCL. The latter had frequent losses of 6q, 17p, 1p and 9p. Chromosome 12p was the most frequent target of deletions among PTLD-DLBCL cases. Loss of heterozygosity (LOH) did not always match DNA loss: chromosome 10 seemed to be targeted by uniparental disomy in PTLD. Small deletions and gains, involving both known (BCL2 and PAX5) and unknown genes (ZDHHC14), were identified. These data suggest that PTLD share, at a lower frequency, common genetic aberrations with DLBCL from immunocompetent patients. The demonstration of 9p13 amplification emphasises the importance of PAX5 in PTLD. The combination of DNA copy number and LOH assessment lead to the hypothesis that uniparental disomy may be a potential mechanism in B-cell lymphomagenesis.

In vitro Epstein-Barr virus-immortalized lymphoma cell line carrying t(9;14)(p13;q32) chromosome abnormality, derived from splenic lymphoma with villous lymphocytes

We herein describe splenic lymphoma with villous lymphocytes (SLVL) carrying t(9;14)(p13;q32). The t(9;14)(p13;q32) is a rare reciprocal chromosome translocation found in a subset of B-cell malignancies, mainly in low-grade non-Hodgkin's lymphomas. In t(9;14)(p13;q32), PAX-5 gene on 9p13 is involved with the immunoglobulin heavy-chain gene on 14q32. It has been thought that the deregulated expression of PAX-5 as a result of t(9;14)(p13;q32) may contribute to abnormal cell proliferation. Although continuous cell lines are invaluable tools for studying lymphomagenesis in the t(9;14)(p13;q32)-bearing lymphomas, establishment of such cell lines is extremely difficult since they are usually mature B-cell malignancies. In an attempt to transform the SLVL cells into a proliferating cell line, we examined the responses of the cells to infection by Epstein-Barr virus (EBV). SLVL cells were found to be susceptible to immortalization by EBV, resulting in a permanent cell line. The cell line, designated SL-15, possessed the t(9;14)(p13;q32). Genotype analysis and immunophenotype profiles confirmed that the cell line arose from the primary lymphoma cells. The cells had characteristic cytoplasmic villi. SL-15 cells has been growing over 2 years equivalent to 350-400 population doubling levels without proliferative crisis that is often observed in EBV-positive lymphoblastoid cell lines. Furthermore, SL-15 cells, when inoculated into nude mice, formed t(9;14)(p13;q32)-bearing tumors with cytoplasmic villi. The validated SLVL-derived cell line provide a useful model system to study molecular biology of t(9;14)(p13;q32)-bearing B-cell malignancies as well as lymphomagenesis of SLVL in vitro and in vivo.

A PANorama of PAX genes in cancer and development

Populations of self-renewing cells that arise during normal embryonic development harbour the potential for rapid proliferation, migration or transdifferentiation and, therefore, tumour generation. So, control mechanisms are essential to prevent rapidly expanding populations from malignant growth. Transcription factors have crucial roles in ensuring establishment of such regulation, with the Pax gene family prominent amongst these. This review examines the role of Pax family members during embryogenesis, and their contribution to tumorigenesis when subverted.

Rarity of IgH translocations in Waldenström macroglobulinemia

Comparatively little is known of the cytogenetics of Waldenström macroglobulinemia (WM). This is primarily due to the low proliferation of the clonal B cells, which precludes conventional karyotyping in many cases. Translocations involving the immunoglobulin heavy chain (IGH) gene at 14q32 are characteristic of many B-cell lymphomas and myelomas. Initial reports suggested that the t(9;14) was characteristic of lymphoplasmacytic lymphoma (the underlying pathological diagnosis in WM), but subsequent studies have failed to confirm the uniqueness of the translocation. To clarify this, we examined 69 cases of WM with interphase fluorescence in situ hybridization and failed to demonstrate an IgH translocation in 67 (97%). We conclude that IGH translocations are not a feature of WM, and the implications of this finding are discussed.

ETV6: a versatile player in leukemogenesis

Alterations of the ets family transcription factor ETV6 (TEL) and the RUNT domain transcription factor RUNX1 (AML1) play pivotal roles in the leukemogenesis of various types of leukemia. While only three fusion partners of RUNX1 namely ETO, ETV6 and MTG16 have been described so far, there is a plethora of ETV6 fusion partners with about 20 partners described so far. Apart from forming fusion genes there are other genetic alterations of ETV6 including deletions, point mutations and possible alterations at the promoter level that might contribute to the malignant phenotype. This review will focus on ETV6 and on the different mechanisms that are used by this gene to cause leukemia.

Primary diffuse large B-cell lymphomas of the central nervous system are targeted by aberrant somatic hypermutation

We have addressed whether aberrant ongoing hypermutation can be detected in the proto-oncogenes PIM1, c-MYC, RhoH/TTF, PAX5, and the tumor-suppressor gene CD95 in primary central nervous system lymphomas (PCNSLs) derived from immunocompetent HIV-negative patients. Nine of 10 PCNSLs analyzed harbored somatic mutations in the PIM1, c-MYC, RhoH/TTF, and PAX5 genes, but not in the CD95 gene, with 8 tumors carrying alterations in at least 2 of these genes. Furthermore, ongoing aberrant mutation was evidenced in a subset of PCNSLs (2 of 3). Although most of the mutations corresponded to base pair substitutions, deletions were also present. The mean mutation frequency was approximately 60-fold lower for these genes compared with the values obtained for immunoglobulin genes in PCNSL. They were increased 2- to 5-fold compared with extracerebral diffuse large B-cell lymphoma (DLBCL). In summary, our data demonstrate aberrant somatic hypermutations at high frequency in the PIM1, PAX5, RhoH/TTF, and c-MYC genes in most PCNSLs. These findings may indicate a pathogenic role for aberrant somatic hypermutation in PCNSL development. In contrast, although mutations were detected in exon 9 of the CD95 gene, the lack of mutations in the 5′ region provides no evidence for the CD95 gene as a target for aberrant somatic mutation.

Three new cases of non-Hodgkin lymphoma with t(9;14)(p13;q32)

The majority of non-Hodgkin lymphomas of B-cell type (B-NHL) exhibit chromosomal abnormalities including many types of reciprocal translocations closely related to specific histopathologic entities. The t(9;14)(p13;q32) has been recognized as a primary genetic event directly involved in the development of lymphoplasmacytic lymphoma. In the 14 published cases, the t(9;14)(p13;32) seems to delineate a variety of low-grade B-cell disorders characterized by a common clinical history and immunopathologic similarities. We report here three new cases presenting a t(9;14)(p13;q32) with other chromosomal abnormalities which have been referred to as B-cell low-grade or high-grade malignant lymphoproliferative disorders. Two of these cases showed diffuse large B cell lymphoma morphology and two patients had a favorable clinical outcome. These data suggest that t(9;14)(p13;q32) is not restricted to low-grade lymphoma.

[Cytogenetic abnormalities in malignant lymphoma and multiple myeloma]

During the past few years, cytogenetic analysis of malignant proliferations contributed to the resolution of complex heterogeneous pathologic groups in smaller well defined entities. This is particularly true in the field of hematologic malignancies, for acute leukemia as well as for Lymphoma, Hodgkin's disease or multiple myeloma. The improvement of knowledge regarding chromosomal or genetic rearrangements involved in the development of these tumors nowadays allows a better understanding of their pathological mechanisms and a better management of the patients.

Waldenström macroglobulinemia neoplastic cells lack immunoglobulin heavy chain locus translocations but have frequent 6q deletions

Lymphoplasmacytic lymphoma (LPL) is characterized by t(9;14)(p13;q32) in 50% of patients who lack paraproteinemia. Waldenström macroglobulinemia (WM), which has an immunoglobulin M (IgM) paraproteinemia, is classified as an LPL. Rare reports have suggested that WM sometimes is associated with 14q23 translocations, deletions of 6q, and t(11;18)(q21;q21). We tested for these abnormalities in the clonal cells of WM patients. We selected patients with clinicopathologic diagnosis of WM (all had IgM levels greater than 1.5 g/dL). Southern blot assay was used to detect legitimate and illegitimate IgH switch rearrangements. In addition to conventional cytogenetic (CC) and multicolor metaphase fluorescence in situ hybridization (M-FISH) analyses, we used interphase FISH to screen for t(9;14)(p13;q32) and other IgH translocations, t(11;18)(q21;q21), and 6q21 deletions. Genomic stability was also assessed using chromosome enumeration probes for chromosomes 7, 9, 11, 12, 15, and 17 in 15 patients. There was no evidence of either legitimate or illegitimate IgH rearrangements by Southern blot assay (n = 12). CC (n = 37), M-FISH (n = 5), and interphase FISH (n = 42) failed to identify IgH or t(11;18) translocations. Although tumor cells from most patients were diploid for the chromosomes studied, deletions of 6q21 were observed in 42% of patients. In contrast to LPL tumors that are not associated with paraproteinemia and that have frequent t(9;14)(p13;q32) translocations, IgH translocations are not found in WM, a form of LPL tumor distinguished by IgM paraproteinemia. However, WM tumor cells, which appear to be diploid or near diploid, often have deletions of 6q21.