The product of the t(11;18), an API2-MLT fusion, is an almost exclusive finding in marginal zone cell lymphoma of extranodal MALT-type

Section E6.1-6.6 of the American College of Medical Genetics and Genomics (ACMG) Technical Laboratory Standards: Cytogenomic studies of acquired chromosomal abnormalities in neoplastic blood, bone marrow, and lymph nodes

Cytogenomic analyses of acquired clonal chromosomal abnormalities in neoplastic blood, bone marrow, and/or lymph nodes are instrumental in the clinical management of patients with hematologic neoplasms. Cytogenetic analyses assist in the diagnosis of such disorders and can provide important prognostic information. Furthermore, cytogenetic studies can provide crucial information regarding specific genetically defined subtypes of these neoplasms that may have targeted therapies. At time of relapse, cytogenetic analysis can confirm recurrence of the original neoplasm, detect clonal disease evolution, or uncover a new unrelated neoplastic process. This section deals specifically with the technical standards applicable to cytogenomic studies of acquired clonal chromosomal abnormalities in neoplastic blood, bone marrow, and/or lymph nodes. This updated Section E6.1-6.6 supersedes the previous Section E6 in Section E: Clinical Cytogenetics of the American College of Medical Genetics and Genomics Technical Standards for Clinical Genetics Laboratories.

Role of Helicobacter pylori in gastric mucosa-associated lymphoid tissue lymphomas

Mucosa-associated lymphoid tissue (MALT) lymphoma is an indolent extranodal marginal zone B-cell lymphoma, originating in acquired MALT that is induced in mucosal barriers as part of a normal adaptive immune response to a chronic immunoinflammatory stimulus, most notably chronic infection by Helicobacter pylori (H. pylori). This antigenic stimulation initially leads to lymphoid hyperplasia; the acquisition of additional genetic aberrations culminates in the activation of intracellular survival pathways, with disease progression due to proliferation and resistance to apoptosis, and the emergence of a malignant clone. There are descriptions of MALT lymphomas affecting practically every organ and system, with a marked geographic variability partially attributable to the epidemiology of the underlying risk factors; nevertheless, the digestive system (and predominantly the stomach) is the most frequently involved location, reflecting the gastrointestinal tract’s unique characteristics of contact with foreign antigens, high mucosal permeability, large extension and intrinsic lymphoid system. While early-stage gastric MALT lymphoma can frequently regress after the therapeutic reversal of the chronic immune stimulus through antibiotic eradication of H. pylori infection, the presence of immortalizing genetic abnormalities, of advanced disease or of eradication-refractoriness requires a more aggressive approach which is, presently, not consensual. The fact that MALT lymphomas are rare neoplasms, with a worldwide incidence of 1-1.5 cases per 10⁵ population, per year, limits the ease of accrual of representative series of patients for robust clinical trials that could sustain informed evidence-based therapeutic decisions to optimize the quality of patient care.

T(14;18)(q32;q21) involving MALT1 and IGH genes occurs in extranodal diffuse large B-cell lymphomas of the breast and testis

Primary B-cell lymphoma of the testis, breast and thyroid are rare and data concerning cytogenetic aberrations at these extranodal sites are scarce. We examined the presence of extranodal marginal zone lymphoma-associated translocations, t(11;18)(q21;q21), t(1;14)(p22;q32), t(14;18)(q32;q21), t(3;14)(p14.1;q32) and numerical aberrations of chromosomes 1, 3, 12 and 18 by fluorescence in situ hybridization in 6 extranodal marginal zone lymphomas and 24 diffuse large B-cell lymphomas with (n=9) or without (n=15) marginal zone lymphoma components, with primary localizations in the breast (n=15), testis (n=9) and thyroid (n=6). We found t(14;18)(q32;q21), with breakpoints in IGH and MALT1, in one testicular diffuse large B-cell lymphoma and in two diffuse large B-cell lymphomas of the breast. No other translocations, amplifications or deletions involving IGH, BCL-10, BCL-2, MALT1 and IAP2 were detected. Numerical aberrations occurred in 67% of the lymphomas, 67% of extranodal marginal zone lymphomas, 56% of diffuse large B-cell lymphomas with marginal zone lymphoma components and in 73% of 'de novo' diffuse large B-cell lymphomas. These included 78% of testis, 67% of thyroid and 60% of breast lymphomas, and included mainly trisomy 18 (n=16), trisomy 3 (n=8) and trisomy 1 (n=3). One testicular diffuse large B-cell lymphoma harbored both t(14;18)(q32;q21) and trisomy 3. Our results indicate that at least a few cases of diffuse large B-cell lymphoma of the testis and the breast belong to the spectrum of extranodal marginal zone lymphoma.

From MALT lymphoma to the CBM signalosome: three decades of discovery

The advent of molecular cytogenetics has led to the elucidation of genetic abnormalities that cause various congenital and oncological disorders. In B cell lymphoma, for example, a number of chromosomal translocations have been identified in and associated with the etiology of specific subtypes of lymphoma. Several recurrent chromosomal translocations have been identified in extranodal marginal zone B cell lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma). Cloning and characterization of the products of three mutually exclusive translocation breakpoints found in MALT lymphoma led to the discovery of a novel NF-κB-activating complex comprising the CARMA, Bcl10, and MALT1 proteins. This "CBM signalosome" acts downstream of the antigen receptors in lymphocytes as well as a number of non-lymphoid cell-surface receptors involved in a variety of biological processes. CBM signalosome activity is important for normal cellular functions and is perturbed in neoplastic and inflammatory disorders, making it a viable target for novel therapeutic design.

Clinical, immunologic, and molecular factors predicting lymphoma development in Sjogren's syndrome patients

Among autoimmune diseases, Sjogren's syndrome (SS) displays the highest incidence of non-Hodgkin lymphoma (NHL) development with the salivary extranodal marginal zone B cell lymphomas being the most common type. The majority of SS-associated NHLs are characterized by localized stage, indolent clinical course, and recurrence in other extranodal sites. Although the transition from a chronic inflammatory condition to malignant lymphoma is a multistep process yet poorly understood, there is increasing evidence that chronic antigenic stimulation by an exoantigen or autoantigens plays an essential role in the development of SS associated lymphoproliferation. Additional molecular oncogenic events such as microsatellite instability, loss of the B cell cycle control, and the forced overproduction of specific B cell biologic stimulators seem to contribute to the emergence and progression of the malignant overgrowth. Among the clinical and serological parameters that have been associated with lymphoma development in SS patients, the presence of palpable purpura, low C4, and mixed monoclonal cryoglobulinemia constitute the main predictive markers, and patients displaying these risk factors should be monitored closely.

The incidence and anatomic site specificity of chromosomal translocations in primary extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) in North America

Several balanced translocations have been identified in extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) but there are few data regarding their frequency in different anatomic sites or the frequency of translocations involving BCL6 or kappa or lambda immunoglobulin light chain genes (IGK or IGL), particularly in patients from geographic regions other than Europe and Japan. One hundred thirty-three paraffin-embedded North American primary MALT lymphoma specimens from diverse anatomic sites were studied by fluorescence in situ hybridization (FISH) using probes for API2-MALT1, IGH-MALT1, IGH-BCL10, IGH-FOXP1, IGH, +/- centromeres 3, 7, 12, and 18, and a subset (n=74) were analyzed using FISH probes for IGK, IGL, and BCL6. Translocations were mutually exclusive and were detected in 26% of cases (17% API2-MALT1, 5% IGH-MALT1, 3% IGH-unknown translocation partner, and 1% IGH-BCL10). Aneuploidy was associated with IGH-MALT1 and IGH-BCL10 but only rarely with API2-MALT1. There was striking site specificity, with API2-MALT1 showing a marked predilection for lung and intestine, and IGH-MALT1 and IGH-BCL10 occurring almost exclusively in lung. Twenty-three percent of translocation-negative primary MALT lymphomas from diverse sites showed complete/partial trisomy 18. No MALT lymphomas with translocations involving IGK, IGL, BCL6, or FOXP1 were identified. This FISH panel detected cytogenetic abnormalities in half of all MALT lymphomas, and translocations arose preferentially in MALT lymphomas of the lung and gastrointestinal tract. Differences in incidence and anatomic site specificity of translocations between North American and non-North American cases may reflect geographic variability of infectious or other etiologic factors.

MALT1, BCL10 and FOXP1 in salivary gland mucosa-associated lymphoid tissue lymphomas

In view of the certain anatomic site-dependent frequency of chromosomal translocations involved in extranodal marginal zone B cell lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) pathogenesis, 17 salivary gland MALT lymphoma cases were analyzed for MALT1 and FOXP1 translocations. B cell CLL/lymphoma 10 (BCL10) and forkhead box PA (FOXP1) protein expression were studied by immunohistochemistry and translocations identified using fluorescence in situ hybridization (FISH)-specific probes FOXP1, t(11;18)(q21;q21)/API2-MALT1 and t(14;18)(q32;q21)/IgH-MALT1. None of the 11 analyzed cases showed FOXP1 rearrangement or amplification. The t(11;18) was present in five of 13 cases and the t(14;18) in three of 13 cases. MALT1 translocations were mostly mutually exclusive except in a single case. FOXP1 protein expression showed differences in the proportion of tumor cells with nuclear expression but not in their intensity, with the exception of one case where very intense nuclear staining was noted. BCL10 nuclear expression was present in four of 17 cases, two of which lacked t(11;18). Our results suggest that MALT1-specific translocations and FOXP1 rearrangements are not commonly involved in pathogenesis. A case with strong FOXP1 protein expression indicates the possibility that the upregulation of FOXP1 expression is significant in a small subset of salivary gland MALT lymphomas. Also a single case in which both MALT1 translocations were present indicates that these are not always mutually exclusive.

Forkhead box protein P1 expression in mucosa-associated lymphoid tissue lymphomas predicts poor prognosis and transformation to diffuse large B-cell lymphoma

PURPOSE

Gene expression profiling studies have reported upregulated mRNA expression of forkhead box protein P1 (FOXP1) in response to normal B-cell activation and high expression in a poor prognosis subtype of diffuse large B-cell lymphoma (DLBCL). Recently, it was also found that FOXP1 rearrangements and expression of its protein occur in mucosa-associated lymphoid tissue (MALT) lymphomas. In this study, we investigated FOXP1 expression in its relationship to morphology, genetic features, and prognosis in a series of 70 MALT lymphomas.

PATIENTS AND METHODS

All samples were morphologically reviewed and stained for FOXP1. Presence of structural and/or numeric aberrations of the FOXP1, BCL10, and MALT1 genes was investigated. For all patients, a complete clinical data set was collected.

RESULTS

We detected nuclear expression of FOXP1 in 20 of the 70 MALT lymphomas (nine of them featuring structural or numeric aberrations of the FOXP1 locus). FOXP1 positivity was confined to MALT lymphomas with poor clinical outcome (with impact of FOXP1 expression on relapse rate and disease-free survival). It was also found that MALT lymphomas with strong FOXP1 expression are at risk of transforming into an aggressive DLBCL of nongerminal center phenotype if they feature, in addition, a polymorphic histology and the presence of trisomy 3 and 18.

CONCLUSION

The data presented show that FOXP1 expression is an independent prognostic factor in MALT lymphomas. The data also support the hypothesis that a subgroup of nongerminal center DLBCLs (those marked by FOXP1 expression and trisomy 3 and 18) might represent a large-cell variant of MALT lymphomas.

MALT1 and BCL10 aberrations in MALT lymphomas and their effect on the expression of BCL10 in the tumour cells

Among the genetic abnormalities reported to occur in mucosa-associated lymphoid tissue (MALT) lymphomas, the three translocations t(11;18)(q21;q21), t(1;14)(p22;q32) and t(14;18)(q32;q21) are of particular interest because they appear to be specific for, or at least closely related to this type of B-cell non-Hodgkin's lymphoma. These translocations affect the MALT1 (18q21) and BCL10 (1p22) genes. We retrieved 77 consecutive biopsies of MALT lymphomas (documented with frozen material) over a 10-year period and investigated these cases for the presence of these three translocations with fluorescence in situ hybridisation, along with the immunohistochemical analysis of the intracellular localisation of the BCL10 protein. The above-listed translocations occurred mutually exclusive and were detected in 10, 1 and 3% of the cases, respectively (the latter incidence being much lower than in the previously reported studies by one single group). These genetic rearrangements corresponded well with the aberrant subcellular localisation of the BCL10 protein as found by immunohistochemistry: t(11;18)(q21;q21) and (1;14)(p22;q32) were marked by a, respectively, moderate to strong nuclear BCL10 staining pattern while t(14;18)(q32;q21)-positive MALT lymphomas were characterised by a perinuclear BCL10 staining pattern. This study further supports the close interaction between the MALT1 and BCL10 proteins in the pathogenesis of MALT lymphomas and may indicate that BCL10 immunohistochemistry is a simple technique to identify those MALT lymphoma cases with an underlying genetic aberration.

FISH analysis of MALT lymphoma-specific translocations and aneuploidy in primary cutaneous marginal zone lymphoma

Primary cutaneous marginal zone lymphomas (PCMZL) share histological and clinical characteristics with mucosa-associated lymphoid tissue (MALT) lymphomas suggesting a common pathogenesis. A number of recurrent structural and numerical chromosomal aberrations have been described in MALT lymphoma, but their incidence in PCMZL is largely unknown, as is their relation with clinical and pathological data. In this study, the incidence of t(11;18)(q21;q21), t(1;14)(p22;q32), two different t(14;18)(q32;q21), involving either IGH/MALT1 or IGH/BCL2, and numerical aberrations of chromosomes 3, 7, 12 and 18 were analysed in 12 patients with PCMZL, with follow-up of up to 10 years. Nuclei were isolated from paraffin wax sections for dual-colour interphase fluorescence in situ hybridization (FISH) using various probe sets either flanking or spanning the involved genes. T(14;18)(q32;q21), with breakpoints in IGH and MALT1, was found in three cases. All three had partly monocytoid histological appearances and lacked blastic transformation. An additional trisomy of chromosome 3 was detected in one of these cases. Trisomy 18 was present in two lymphomas without monocytoid morphology. No definite correlation was seen with any clinical feature, including Borrelia serology. Neither t(11;18)(q21;q21), nor t(1;14)(p22;q32) or any other translocation involving IGH, BCL10, MALT1, BCL2 and API2, amplification or deletion of chromosomal region 11q21, 18q21, 1p22, and 14q32 was detected. These results indicate that a subgroup of PCMZL with partly monocytoid morphology is genetically related to MZL at other extranodal sites.

Chromosome 18 suppresses tumorigenic properties of human prostate cancer cells

Although prostate cancer is still the most diagnosed cancer in men, most genes implicated in its progression are yet to be identified. Chromosome abnormalities have been detected in human prostate tumors, many of them associated with prostate cancer progression. Indeed, alterations (including deletions or amplifications) of more than 15 human chromosomes have been reported in prostate cancer. We hypothesized that transferring normal human chromosomes into human prostate cancer cells would interfere with their tumorigenic and/or metastatic properties. We used microcell-mediated chromosome transfer to introduce human chromosomes 10, 12, 17, and 18 into highly tumorigenic (PC-3M-Pro4) and highly metastatic (PC-3M-LN4) PC-3-derived cell lines. We tested the in vitro and in vivo properties of these hybrids. Introducing chromosome 18 into the PC-3M-LN4 prostate cancer cell line greatly reduced its tumorigenic phenotype. We observed retarded growth in soft agar, decreased invasiveness through Matrigel, and delayed tumor growth into nude mice, both subcutaneously and orthotopically. This phenotype is associated with a marker in the 18q21 region. Combined with the loss of human chromosome 18 regions often seen in patients with advanced prostate cancer, our results show that chromosome 18 encodes one or more tumor-suppressor genes whose inactivation contributes to prostate cancer progression.

Frequency of Chromosomal Aberrations Involving MALT1 in Mucosa-Associated Lymphoid Tissue Lymphoma in Patients with Sjögren’s Syndrome

PURPOSE

Mucosa-associated lymphoid tissue (MALT) lymphoma develops in the context of longstanding antigenic stimulation such as infection with Helicobacter pylori or autoimmune disease, including Sjögren's syndrome (SS). Recently, two chromosomal aberrations involving the MALT1 gene, i.e., t(11;18)(q21;q21) and t(14;18)(q32;q21) have been reported as genetic events specific for MALT lymphoma. In view of the association between SS and the development of MALT lymphoma, we have analyzed the frequency of t(11;18)(q21;q21) and t(14;18)(q32;q21) in patients with MALT lymphomas arising in the background of SS.

EXPERIMENTAL DESIGN

A retrospective analysis of patients diagnosed with MALT lymphoma and SS was performed. The t(11;18)(q21;q21) was analyzed using reverse transcriptase-PCR, whereas t(14;18)(q32;q21) was assessed by two-color interphase fluorescence in situ hybridization.

RESULTS

Twenty-six patients (20 female and 6 male) with MALT lymphoma and SS could be identified. The lymphoma was located in the parotid (n = 14), orbit (n = 2), and submandibular gland (n = 1), whereas 9 patients had gastric MALT lymphoma. Seven of 26 patients (27%) harbored t(11;18)(q21;q21). Interestingly, only 1 of 17 patients (6%) with extragastrointestinal lymphoma was positive, as opposed to 6 of 9 patients (67%) with gastric MALT lymphoma. Four of 26 patients were positive for t(14;18)(q32;q21): 3 of 17 extragastrointestinal (18%) and 1 of 9 gastric lymphomas (11%).

CONCLUSIONS

The overall frequency of MALT1 rearrangement appears to be low in patients with extragastrointestinal MALT lymphoma associated with SS. By contrast, MALT1 rearrangement was demonstrated in 7 of 9 patients (78%) with gastric MALT lymphoma and SS. This finding may explain at least in part why gastric MALT lymphomas in patients with SS are refractory to H. pylori eradication therapy.

Localized mucosa-associated lymphoid tissue lymphoma treated with radiation therapy has excellent clinical outcome

PURPOSE

Extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) is a distinct lymphoma with unique clinicopathologic features. We report the clinical outcome of stage I and II MALT lymphoma treated with involved field radiation therapy (RT).

PATIENTS AND METHODS

From 1989 to 2000, 103 patients with stage IE and IIE disease were referred. Their median age was 60 years, with a 2:1 female predominance. Presenting sites were stomach (17 patients), orbital adnexa (31 patients), salivary glands (24 patients), thyroid gland (13 patients), and other sites (18 patients). Ninety-three patients received RT--85 received RT alone, and eight received chemotherapy and RT--with a median dose of 30 Gy. The median follow-up time was 5.1 years.

RESULTS

A complete response (CR) to RT alone was achieved in 84 of 85 patients. Among CR patients, 14 experienced relapse. Relapse sites were mostly contralateral paired-organ or distant MALT locations and, infrequently, lymph nodes. The crude local control rate with RT was 95.3% (81 of 85 patients). No relapses were observed in patients with stomach or thyroid lymphoma, whereas 14 of 63 patients (22%) experienced relapse in the other sites. The overall 5-year survival rate was 98%, and the disease-free survival rate was 77%. Transformed lymphoma was observed in 14% of patients (two of 14) experiencing relapse.

CONCLUSION

Moderate-dose RT achieved excellent local control in localized MALT lymphomas and had curative potential for three fourths of the patients. Gastric and thyroid MALT lymphomas had better outcome, whereas distant failures were common for other sites. Despite relapse, the disease often maintained an indolent course.

Mutual exclusion of t(11;18)(q21;q21) and numerical chromosomal aberrations in the development of different types of primary gastric lymphomas

Gastric non-Hodgkin's lymphomas can be divided histologically into mucosa-associated lymphoid tissue (MALT) lymphoma (ML) and diffuse large cell lymphoma (DLCL) with or without evidence of preceding/accompanying ML (DLCL + ML). We studied the incidence of the most frequent structural chromosomal aberration in ML, t(11;18)(q21;q21), and numerical aberrations of seven chromosomes in 36 ML, 39 DLCL + ML and ten gastric DLCL cases, by dual-colour interphase fluorescence in situ hybridization (FISH) and reverse transcriptase polymerase chain reaction (RT-PCR). t(11;18)(q21;q21) was exclusively detected in ML (FISH 22%; RT-PCR 24%), being completely absent in DLCL + ML and DLCL. No other translocations involving 11q21 or 18q21 and other partner chromosomes were detected by FISH. In lymphomas harbouring t(11;18)(q21;q21), this translocation was the sole genetic abnormality. In contrast, 45% of the t(11;18)(q21;q21)-negative ML showed trisomies, especially of chromosome 3 and 18. In DLCL + ML with separate small and large cell components, trisomies were either detected in both components or occurred exclusively in large tumour cells. Our results suggest that ML can be divided in lymphomas characterized by the t(11;18)(q21;q21), which are unlikely to transform into high-grade tumours, and t(11;18)(q21;q21)-negative ML that may develop into DLCL + ML after the acquisition of additional genetic aberrations.

Primary pulmonary MALT lymphomas show frequent and heterogeneous cytogenetic abnormalities, including aneuploidy and translocations involving API2 and MALT1 and IGH and MALT1

API2-MALT1 fusion and aneuploidy are common chromosomal abnormalities in MALT lymphoma. In studying their incidence and relationship in primary pulmonary MALT lymphomas, a translocation involving MALT1 and IGH was also identified. In all, 28 primary pulmonary MALT lymphomas were studied by fluorescence in situ hybridization using an API2-MALT1 probe and multiple centromeric probes, as well as IGH-BCL2, IGH-MALT1, and MALT1 breakapart probes in selected cases. Seven (25%) had API2-MALT1 fusion; all seven lacked aneuploidy except for two with trisomy 3 in a small clone. Three (11%) had IGH-MALT1 fusion; two also showed trisomy 3 and 12. A total of 11 (39%) had aneuploidy only, with trisomy 3 and 18 being the most common. Ectopic nuclear bcl-10 expression, which has been previously associated with API2-MALT1, was seen by immunohistochemistry in 86% of API2-MALT1 fusion-positive cases, one IGH-MALT1 fusion-positive case, two aneuploidy-only cases, and two normal cases. In primary pulmonary MALT lymphomas, cytogenetic abnormalities are common (75%) and heterogeneous, encompassing API2-MALT1 and IGH-MALT1, which are mutually exclusive, as well as aneuploidy, which may be present in the latter but is rare in the former. Ectopic nuclear bcl-10 expression is associated with API2-MALT1 but may also be seen in IGH-MALT1 fusion-positive, aneuploidy-only, and normal cases.

Heterogeneous copy numbers of API2-MALT1 chimeric transcripts in mucosa-associated lymphoid tissue lymphoma

T(11;18)(q21;q21) results in a chimeric transcript between API2 at 11q21 and MALT1 at 18q21 and is a characteristic chromosomal aberration of extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma). API2-MALT1 chimeric transcripts are present in approximately one-third of all cases of MALT lymphoma. MALT lymphoma is also known to have variations in histological features and tumor cell proportions. Real-time polymerase chain reaction (PCR) was used to examine number of API2-MALT1 copies in clinical samples for further investigation of the pathophysiology of MALT lymphoma. A total of 13 samples of MALT lymphoma contained API2-MALT1 transcripts from 1.7 x 10(-2) to 1.0 copies/beta-actin copy. These findings were compared to the proportions of tumor cells in genomic VDJ PCR products determined by Southern blotting. Tumor cell ratios varied widely among the patients' samples, and no significant correlation was found between transcript copy number and tumor cell ratio. These results suggest that copy numbers of API2-MALT1 do not reflect tumor cell proportions, and that the number of copies of API2-MALT1 in a tumor cell is different for each clinical sample.

[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.

Splenic marginal zone lymphoma

Splenic marginal zone lymphoma (SMZL) is an indolent lymphoproliferative disease accounting for approximately 1% of all lymphomas. SMZL presents with marked splenomegaly, and often accompanied by circulating atypical 'villous lymphocytes' and is also known as splenic lymphoma with villous lymphocytes. Histologically, the spleen in SMZL is characterised by a nodular infiltrate based on pre-existing white pulp but also involving the red pulp. Within the white pulp, the infiltrate has a biphasic morphology comprising an inner zone of small lymphocytes and a peripheral (marginal) zone of larger lymphoid cells. Usually the splenic lymph nodes and bone marrow are also involved by a vaguely nodular infiltrate of similar nature. Immunophenotypically, the tumor cells has a mature B-cell phenotype and frequently express IgM and IgD but typically lack CD5, CD23, CD43, CD10, Bcl-6 and cyclin D1. Analysis of immunoglobulin heavy-chain gene variable regions suggest that some cases of SMZL arise form postfollicular B cells but others from naïve B cells. Genetic studies have shown abnormalities of a number of chromosomes however 7q31-32 allelic loss appears to be characteristic. Histological differential diagnosis include a number of entities such as lymphoid hyperplasias, other marginal zone lymphomas, mantle cell lymphoma, follicular lymphoma, and B-CLL.

Splenic marginal zone lymphoma

Splenic marginal zone lymphoma (SMZL) is a specific low-grade small B-cell lymphoma that is incorporated in the World Health Organization classification. Characteristic features are splenomegaly, moderate lymphocytosis with villous morphology, intrasinusoidal pattern of involvement of various organs, especially bone marrow, and relative indolent course. Tumor progression with increase of blastic forms and aggressive behavior are observed in a minority of patients. Molecular and cytogenetic studies have shown heterogeneous results probably because of the lack of standardized diagnostic criteria. To date, no definitive therapy has been established. Therapeutic options include treatment abstention, splenectomy, splenic irradiation, and chemotherapy.

Marginal zone cell lymphoma--an update on recent advances

The marginal zone represents one of the distinct compartments of the B-cell area in lymphoid tissues. It is especially well developed in the spleen and in Peyer's patches of the gut, but not in lymph nodes, with the exception of the ones in the mesenterium. However, the pronounced proliferation of so-called 'monocytoid B-cells' that may be seen in some inflammatory conditions of the lymph node may be regarded as a nodal reactive marginal zone cell expansion. The cellular compositions of the marginal zone and the monocytoid B-cell proliferation are similar and both show a heterogeneous population of B-cells, of which the functions are being slowly unravelled. Neoplasms originating in the marginal zone have been recognized in the past and are listed in the REAL classification as marginal zone B-cell lymphomas including extranodal MALT-type lymphomas, splenic marginal zone lymphomas and nodal (monocytoid) marginal zone lymphomas. Marginal zone cell lymphomas display a broad morphological spectrum, which is reflected by the heterogeneity of the cellular composition and the variation in the growth pattern of the lymphoma, but is independent of the anatomical site. All three marginal zone cell lymphomas share immunophenotypic, genetic and chromosomal similarities which will be discussed. The morphologic features are dealt with only briefly as they have been extensively discussed elsewhere.

Mucosa-associated lymphoid tissue lymphoma

Since the first description of mucosa-associated lymphoid tissue (MALT) lymphoma in 1983 rapid advances have been made in the understanding of the pathogenesis and underlying molecular events associated with the development of this tumor. Lymphoma arises at extranodal sites in which a pre-existing inflammatory response has provoked the acquisition of organized lymphoid tissue. Specific molecular events have been associated with the development of MALT lymphoma including t(11;18) and alterations in Bcl-10 protein expression, and these appear to be interlinked. In gastric MALT lymphoma Helicobacter pylori is the most common stimulus for the acquisition of lymphoid tissue. Eradication of this organism has been shown to result in regression of the tumor in many cases, but there are a few that will not respond to this approach. Predicting those cases unlikely to respond to H pylori eradication alone has been investigated in a number of ways. An underlying t(11;18) within the tumor cells appears to predict for a lack of response. Clinical measurement of the depth of infiltration of the wall by gastric MALT lymphoma as measured by endoscopic ultrasound has been less clear. More superficial tumors are more likely to respond, but regression has been reported even in cases with local lymph node involvement. For superficial lymphomas at other sites alternatives to radiotherapy, chemotherapy, or surgery have been sought. Local injections of interferon (IF) alpha have been successful in treating conjunctival lymphoma, and this approach may be of use for other superficial lesions.

Detection of AP12-MALT1 chimaeric gene in extranodal and nodal marginal zone B-cell lymphoma by reverse transcription polymerase chain reaction (PCR) and genomic long and accurate PCR analyses

t(11;18)(q21;q21) has been recognized as a characteristic chromosomal translocation in mucosa-associated lymphoid tissue (MALT)-type lymphoma, and recent studies have demonstrated that this translocation results in the chimaeric transcript of API2 (apoptosis inhibitor 2)-MALT1 (mucosa-associated lymphoid tissue lymphoma translocation gene 1). In this study, we used reverse transcription polymerase chain reaction (RT-PCR) to analyse the incidence of this fusion product in a large series of MALT lymphoma, nodal marginal zone B-cell lymphoma (nMZBCL) and extranodal diffuse large B-cell lymphoma (DLBL) cases. RT-PCR analysis revealed that 17 of the 95 (17.9%) MALT lymphomas but none of the nine nMZBCLs or 16 DLBLs had API2-MALT1 fusion transcripts. The incidence of API2-MALT1 varied among MALT lymphomas arising from different sites and was highest for pulmonary MALT lymphomas (10 out of 16 cases, 62.5%). The presence of the API2-MALT1 fusion gene was also confirmed by long and accurate (LA)-PCR with genomic DNA, and the result correlated well with that obtained with the RT-PCR assay, thus demonstrating the usefulness of LA-PCR for the detection of the API2-MALT1 fusion gene.

Stage I and II MALT lymphoma: results of treatment with radiotherapy

PURPOSE

Mucosa-associated lymphoid tissue (MALT) lymphoma is a distinct disease with specific clinical and pathologic features that may affect diverse organs. We analyzed our recent experience with Stage I/II MALT lymphoma presenting in the stomach and other organs to assess the outcome following involved field radiation therapy (RT).

PATIENTS AND METHODS

Seventy patients with Stage IE (62) and IIE (8) disease were treated between 1989 and 1998. Patients with transformed MALT were excluded. The median age was 62 years (range, 24--83 years), M:F ratio 1:2.2. Presenting sites included stomach, 15; orbital adnexa, 19; salivary glands, 15; thyroid, 8; lung, 5; upper airways, 3 (nasopharynx, 2; larynx, 1); urinary bladder, 3; breast, 1; and rectum, 1. Staging included site-specific imaging, CT abdomen in 66 patients (94%) and bone marrow biopsy in 54 (77%). Sixty-two patients received radiation therapy: 52 received RT alone, 7 received chemotherapy and RT, and 3 received antibiotics followed by RT. Median RT dose was 30 Gy (range, 17.5--35 Gy). Most frequently used RT prescriptions were 25 Gy (26 patients-18 orbit, 6 stomach, and 2 salivary glands), 30 Gy (23 patients), and 35 Gy (8 patients). Five patients had complete surgical excision of lymphoma and no other treatment (stomach 1, salivary 2, lung 2), whereas 2 patients with gastric lymphoma received antibiotics only. One patient refused treatment and was excluded from the analysis of treatment outcome, leaving 69 patients with a median follow-up of 4.2 years (range, 0.3-11.4 years).

RESULTS

A complete response was achieved in 66/69 patients, and 3 patients had partial response (2 lung, 1 orbit). The 5-year disease-free survival (DFS) was 76%, and the overall survival was 96%. No relapses were observed in patients with stomach and thyroid lymphoma. The 5-year DFS for these patients was 93%, in contrast to 69% for patients presenting in other sites (p = 0.006). Among the 5 patients treated with surgery only, 2 relapsed locally (lung, and minor salivary gland). Among 62 patients who received RT, 8 relapsed (2 salivary, 3 orbit, 1 nasopharynx, 1 larynx, 1 breast). Three patients relapsed in the nonirradiated contralateral paired organ, 4 in distant sites, and 1 in both local and distant sites. The overall local control rate with radiation was 97% (60/62 patients).

CONCLUSION

Localized MALT lymphomas have excellent prognosis following moderate-dose RT. Gastric and thyroid MALT lymphomas have better early outcome, as compared to the other sites where distant failure is more common. Relapses were observed in nonirradiated paired organs or distant sites. Further follow-up is required to assess the impact of failure on survival.

Structure of the MLT gene and molecular characterization of the genomic breakpoint junctions in the t(11;18)(q21;q21) of marginal zone B-cell lymphomas of MALT type

The t(11;18)(q21;q21) between the inhibitor of apoptosis API2 and the MLT gene is a distinct feature of marginal zone B-cell lymphomas of MALT-type. Hitherto the chimeric API2-MLT transcripts are all "in-frame" and predominantly fuse exon 7 of API2 to different MLT exons. Recurrent chromosomal translocations are common in lymphoid neoplasms and might represent by-products of the rearrangement processes generating antigen receptor diversity. The genomic structure of the MLT gene was determined to facilitate amplification of the genomic breakpoint junctions from 5 MALT-type lymphomas with t(11;18). Their sequence analysis showed scattering of the chromosome 11 breakpoints in intron 7 of API2 whereas rearrangements in MLT occurred in intron 2, 4, 7, or 8, respectively. Sequences around the junctions did not display recognition signal sequences mediating lymphocytic V(D)J recombination or other sequence motifs associated with recombination. The breakpoints occurred in a copy of an AluSx repeat in three cases, but interchromosomal Alu-mediated homologous recombination could be ruled out as the repeat resided only on one of the participating chromosomes. The t(11;18) was associated with a deletion in 4 out of 5 cases, ranging in size from 53 bp up to more than 200 kb. These deletions were observed on one or sometimes both derivative chromosomes that might indicate the susceptibility of these regions for breakage. Our data suggest that the API2-MLT fusion might result from a non-homologous end joining event after multiple double-strand breaks. The clustering of breaks in intron 7 of API2 and the consistent "in frame" API2-MLT fusions could therefore reflect certain functional constraints crucial for clonal outgrowth.