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Mucosa-associated lymphoid tissue (MALT) lymphoma mainly consists of three types of tumor B cells, small (centrocyte-like), scattered large transformed, and intraepithelial. However, it is difficult to differentiate tumor B cells from reactive B cells at the cellular level. We examined five cases of API2-MALT1 fusion-positive MALT lymphoma of the lung. A single paraffin section for each case was subjected to sequential retrieval of whole-slide imaging (WSI) data of hematoxylin and eosin (HE) staining, immunofluorescence staining for CD79a, and fluorescence in situ hybridization (FISH) for the MALT1 split. We counted the number of MALT1 split-positive or MALT1 split-negative cells among CD79a-positive cells. The MALT1 split was detected in 59, 46, and 76 % of small, large, and intraepithelial B cells, respectively. A review of the HE-WSI data showed that cytomorphological distinction between the MALT1 split-positive and MALT1 split-negative B cells was virtually impossible. None of CD79a-negative lymphoid cells, epithelial cells, and microvascular endothelial cells was positive for MALT1 splits. As API2-MALT1 fusion is an early and critical event in the lymphomatogenesis, our findings are best interpreted as that a considerable number of B cells, either small, large, or intraepithelial, are reactive cells and that it is difficult to distinguish cytomorphologically between tumor B cells and reactive B cells. These findings suggest that the tumor architecture may be the central factor for making a correct histopathological diagnosis of MALT lymphoma. The sequential WSI of HE staining, immunofluorescence staining, and FISH as described here is a useful tool for pathological analysis at the cellular level.

Although rare, thymic mucosa-associated lymphoid tissue (MALT) lymphoma is considered to be a distinct clinicopathological entity. Using a methylation-specific polymerase chain reaction, we analyzed thymic MALT lymphomas (n = 18) for their methylation of the following seven tumor suppressor genes: DAPK1, p16(INK4A), p14(ARF), CDH1, RARB, TIMP3 and MGMT. Reactive lymph nodes (n = 16) were used as a control. Of the seven genes examined, thymic MALT lymphomas had an increased number of genes that were methylated (2.9 genes) as compared with reactive lymph nodes (0.63, p = 0.0003). In particular, thymic MALT lymphomas showed a frequent methylation of DAPK1, CDH1, TIMP3 and p14(ARF). In addition, gene methylation of p14(ARF) was associated with a larger tumor size, while that of the other three genes was not associated with any clinicopathological features examined. This study suggests that methylation of tumor suppressor genes may play an important role in thymic MALT lymphoma.

Aims: Diffuse large B cell lymphoma (DLBCL) occasionally shows an interfollicular pattern of proliferation (DLBCL-IF) preserving lymphoid follicles. In this study, clinicopathological findings in 31 cases of DLBCL-IF were analysed., Methods and Results: The study group comprised 20 males and 11 females, with ages ranging from 41 to 87 (median 69) years. The primary site was lymph node in 25 cases, and unknown in six due to advanced stage at diagnosis. Eight cases were clinical Stage I, 10 were Stage II, four Stage III, and nine Stage IV. A polymorphous pattern of proliferation containing large B cells and inflammatory cells was found in about 60% of cases. The overall survival rate of the DLBCL-IF patients was better than that of a DLBCL control group (log-rank test; P < 0.05). Multivariate analysis revealed that an interfollicular pattern of proliferation showed marginal significance for favourable prognosis (P = 0.069). Immunohistochemical double staining with antibodies for HLA-DR/CD68 (markers for M1-tumour-associated macrophage [M1-TAM]) or CD163/CD68 (M2-TAM) revealed that all DLBCL-IF patients with a low M2 count were alive at the end of observation., Conclusions: These findings suggest that DLBCL-IF is a clinicopathological entity distinct from ordinary DLBCL. The possible origin of tumour cells in DLBCL-IF from marginal zone B cells is discussed., (© 2012 Blackwell Publishing Ltd.)

Mucosa-associated lymphoid tissue (MALT) lymphoma arising in the thymus is a rare disorder that shows a strong association with autoimmune disease. Several MALT-lymphoma-specific and -associated chromosomal abnormalities, including t(11;18), t(14;18), t(1;14), trisomy 3 and trisomy 18, are known to occur. The former translocation results in apoptosis inhibitor 2 gene (API2)-MALT lymphoma-associated translocation 1 (MALT1) fusion. In this study, we examined 14 cases of thymic MALT lymphomas for API2-MALT1 fusion using multiplex reverse transcription polymerase chain reaction and looked for trisomy 3, trisomy 18 and abnormalities of MALT1 and IGH genes using fluorescence in situ hybridization. Thymic MALT lymphoma cases had a high frequency of trisomy 3 (7/14 cases), a very low incidence of trisomy 18 (1/14) and no detectable MALT1-associated (0/13) or IGH-associated (0/13) gene abnormalities including t(11;18). A review of the literature showed that the pattern of chromosomal aberrations in thymic MALT lymphoma was similar to those of thyroid and salivary gland MALT lymphomas. Although frequently detected, trisomy 3 was not associated with any of the clinicopathological factors analyzed, suggesting that trisomy 3 may play a role in lymphoma development. In conclusion, the present study showed that thymic MALT lymphoma has a characteristic pattern of chromosomal aberrations that may be similar to those of other autoimmune-associated MALT lymphomas., (© 2011 The Authors. Pathology International © 2011 Japanese Society of Pathology and Blackwell Publishing Asia Pty Ltd.)

The human epidermal growth factor (EGF) receptor (HER) family consists of four receptors that bind to ligands sharing an EGF-like motif. The HER family of receptor tyrosine kinases and their ligands (EGF family) are known to play a significant role in gastrointestinal cancer. In particular, the EGF receptor, HER1, is one of the main candidates for the molecular-targeted therapy of colon cancer, and HER2 is a candidate for the treatment of gastric cancer which overexpresses HER2. In contrast, the role of the HER and EGF families in malignant lymphoma has not been fully elucidated. In this study, we investigated the expression and function of the HER and EGF families in lymphoma cell lines and tumor samples. Reverse transcription polymerase chain reaction revealed that the ligands for HER1 were mainly expressed in gastric cancer and colon cancer cell lines, but not in lymphoma cell lines. On the other hand, the EGF family member, neuregulin (NRG) 4, was highly expressed in lymphoma cell lines. Immunohistochemical analyses of malignant lymphoma clinical samples revealed that NRG4 and HER4 were mainly expressed in mucosa-associated lymphoid tissue (MALT) and follicular lymphoma. Immunoprecipitation of Raji and Daudi cell lines revealed that recombinant NRG4 induced the tyrosine phosphorylation of HER4. Additionally, recombinant NRG4 activated the proliferation of lymphoma cell lines. These findings suggest that the NRG4-HER4 axis plays a major role in the proliferation of malignant lymphoma cells in the gastrointestinal tract.

Pulmonary mucosa-associated lymphoid tissue lymphoma is unique in that chronic inflammation is rare and that API2-MALT1 fusion, resulting from t(11;18)(q21;q21), occurs frequently. In this study, we examined 20 cases for API2-MALT1 fusion using the multiplex reverse-transcription polymerase chain reaction and looked for trisomy 3, trisomy 18, and abnormalities of MALT1 and IGH genes using fluorescence in situ hybridization. In addition, we analyzed VH genes by subcloning of the monoclonal polymerase chain reaction products. Of 20 cases studied, we detected gene abnormalities in 16: API2-MALT1 fusion in 9, trisomy 3 in 5, trisomy 18 in 4, MALT1 abnormality in 13, and IGH abnormality in 1. MALT1 gene abnormalities were concordant with API2-MALT1 fusion or trisomy 18. One case showed API2-MALT1 fusion and trisomy 3. On detection of API2-MALT1 fusion and trisomies, we were able to divide our cases into 3 groups, API2-MALT1 positive, trisomy positive, and no detectable gene abnormality, suggesting that tumor development had processed along different genetic pathways. All 20 cases were analyzed for VH genes. Most of the VH genes selected by the lymphomas belonged to the VH3 family, but there was no restriction to any particular VH fragment. Of interest, VH genes were unmutated in 7 cases, suggesting that T-cell-independent extrafollicular B-cell maturation may be important in the development of this lymphoma. In addition, both mutated and unmutated tumor cases were found to carry the API2-MALT1 fusion and trisomy 3. This observation suggests that these gene abnormalities may occur in microenvironments found before or outside of follicular germinal centers., (Copyright © 2011 Elsevier Inc. All rights reserved.)

A 76-year-old woman was admitted to our hospital with infiltrations evident in the right lower lobe on chest computed tomography. Bronchoscopic biopsy showed lymphoma of mucosa-associated lymphoid tissue (MALT). Lymphoma of the pulmonary MALT became enlarged at 8 months after diagnosis and dyspnea developed. Four courses of chemotherapy(rituximab+ cladribine)resulted in a partial response. However, 14 months after the chemotherapy, she developed multiple lung and liver tumors accompanied by disseminated intravascular coagulation syndrome. A histological examination of bone marrow aspiration showed small cell carcinoma. We administered one course of carboplatin and etoposide, but bone marrow suppression was so severe that further chemotherapy was precluded. To our knowledge, this is a rare case of small cell lung cancer arising from the treatment of lymphoma of pulmonary MALT.

Primary cutaneous marginal zone B-cell lymphoma is considered the cutaneous counterpart of extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue. Although its molecular pathogenesis is currently unknown, an etiological link with Borrelia burgdorferi infection has been identified in European, but not in American or Asian cases. To better understand the pathogenesis and the geographical differences of cutaneous marginal zone B-cell lymphoma, 60 cases from the East Asia, Germany, and the United States at their initial presentation were subjected to the following analyses; (1) clinicopathological comparison between the geographical regions, (2) detection of B. burgdorferi DNA, (3) detection of the API2-MALT1 fusion transcript, a gene alteration specific to mucosa-associated lymphoid tissue lymphoma, and (4) inactivation of tumor suppressor genes (death-associated protein kinase (DAPK), p16(INK4a), p14(ARF), MGMT, TIMP3, CDH1, and RARB) by hypermethylation of the CpG islands. Cases from the three geographical regions showed similar clinicopathological features. However, moderate/marked tissue eosinophilia was found in 9/25 Asian cases, but only 1/23 German cases (P=0.011) and 0/12 American cases (P=0.015). All 60 cases were negative for either Borrelia DNA or API2-MALT1 fusion. Tumors from the three regions were highly methylated for DAPK (38-50% of the cases, mean 43%) and p16(INK4a) (42-70%, mean 49%), and the positivities were significantly higher than those of nonneoplastic skin (8%, P=0.0010 and 14%, P=0.0032, respectively). Methylation of these genes had no significant association with progressive features of the tumor. Primary cutaneous marginal zone B-cell lymphomas from the three geographical regions have common clinicopathological features, however, moderate/marked tissue eosinophilia is a feature found almost exclusively in Asian cases. Borrelia infection and API2-MALT1 fusion are not significant in this tumor. Methylation of DAPK and p16(INK4a) genes is a frequent event in this lymphoma at its initial presentation, but may not be associated with tumor progression.

Primary mucosa-associated lymphoid tissue (MALT) lymphoma of the prostate is rare, and only five cases have been reported. Reported herein is a new case that has involved a 9 year follow up. A 79-year-old man was treated with transurethral resection (TUR) for a mass of the right prostatic lobe, and followed up under a diagnosis of benign prostatic hyperplasia with atypical lymphoid infiltration. Seven years later TUR was again performed for a right lobe mass. The lesion was diagnosed as a relapsed MALT lymphoma after detailed histological and immunoglobulin heavy chain gene analyses of the initial and relapsed lesions. Interestingly, lymphoepithelial lesions were observed only infrequently in this tumor. The API2-MALT1 fusion, a gene alteration specific to MALT lymphoma, was absent. The patient had stage IA disease at the time of tumor relapse, and has been alive and well for the 2 years after the second TUR. The present case suggests that despite tumor recurrence, prostatic MALT lymphoma is indolent, and function-preserving therapy is warranted.

Mucosa-associated lymphoid tissue (MALT) lymphoma is a low-grade tumor closely associated with chronic inflammation such as that of Helicobacter pylori gastritis, Sjogren's syndrome, and Hashimoto's thyroiditis. Tumor regression by H. pylori eradication alone is well known in gastric MALT lymphoma, but some tumors occur in the absence of pre-existing chronic inflammation. The understanding of MALT lymphoma biology has significantly improved, and recurrent cytogenetic alterations have been detected. These include the trisomies 3 and 18, and the translocations t(11;18)(q21;q21), t(1;14)(p22;q32), t(14;18)(q32;q21), and t(3;14)(p14.1;q32). At least some of these alterations result in the constitutive activation of the nuclear factor (NF)-kappaB pathway, and may exert anti-apoptotic action. Apoptosis inhibitor 2-MALT lymphoma-associated translocation 1 (API12-MALT1) fusion, resulting from t(11;18)(q21;q21), is specific to, and is the most common in, MALT lymphomas, and its clinicopathological significance has been studied extensively. The focus of the present review is on the recent progress made in elucidating MALT lymphomagenesis and its clinicopathological impact, especially in terms of the effect of API2-MALT1 fusion on this unique tumor.

The majority of gastric mucosa-associated lymphoid tissue (MALT) lymphomas are successfully treated with Helicobacter pylori eradication alone. However, certain subsets of these tumors are resistant to the eradication treatment. As API2-MALT1 fusion is a feature of one of these subsets, we divided gastric MALT lymphomas into three groups: eradication-responsive and API2-MALT1 fusion-negative (Group A), eradication-resistant and fusion-negative (Group B), and eradication-resistant and fusion-positive (Group C). To characterize further gastric MALT lymphomas, we analyzed VH genes, which do not change in the course of tumor progression, by extensive subcloning of the monoclonal PCR products of 45 cases. VH3-23 and VH3-30 were preferentially used in Group A tumors (14/23 cases, 61%) as compared with Group B (1/10 cases, 10%, P=0.0094) and Group C (2/12 cases, 17%, P=0.017). Tumors of Groups B and C used variegated VH fragments, and no dominant VH fragments were noted. Somatic mutation was detected in most of the cases. Ongoing mutation was detected in 3/45 cases (7%), when assessed according to strict criteria for a confirmed mutation. These findings suggest that inflammation-dependent tumors (Group A) may be derived from a highly restricted, probably H. pylori-associated, B cell subset and may not often progress to those that are inflammation-independent (Groups B and C). Although considered to be common in this tumor, ongoing mutation may be infrequent when assessed by strict criteria.

Primary mucosa-associated lymphoid tissue (MALT) type lymphoma arising in the oral cavity is rare. We examined histopathologic, immunohistological and genotypic findings of seven cases of intraoral MALT lymphoma using formalin-fixed paraffin-embedded tissues. Histologically, two variants have been delineated. (i) In four cases of minor salivary gland type, the lymphoid follicles were surrounded by centrocyte-like (CCL) cells with occasional follicular colonization. The CCL cells invaded the residual salivary gland duct resulting in a lymphoepithelial lesion. CCL cells frequently showed plasmacytic differentiation. (ii) In three cases of follicular growth type, the lesion was characterized by follicular growth pattern resulting from prominent follicular colonization. CCL cells showed minimal plasma cell differentiation. There was no residual epithelial component detected even by cytokeratin immunostaining. There were no Epstein-Barr virus-encoded small RNA-positive cells detected by in situ hybridization. API2-MALT1 fusion transcript does not appear to be associated with either histological variant of primary intraoral MALT lymphoma.

Primary low-grade mucosa-associated lymphoid tissue (MALT) lymphoma of the stomach has a potential to transform to high-grade diffuse large B-cell lymphoma (DLBCL). However, the clonal relation between MALT lymphoma and de novo DLBCL is still controversial. We report here three patients with Helicobacter pylori (H. pylori)-positive gastric MALT lymphoma rapidly progressing to DLBCL at the same site after successful eradication of H. pylori. Although MALT lymphomas in our cases did not possess t(11; 18)(q21;q21), sequence analysis of the rearranged immunoglobulin heavy chain gene showed no clonal relation between preceding MALT lymphoma cells and de novo DLBCL cells at the same site. These findings question the scenario of direct clonal progression of low-grade MALT lymphomas without t(11; 18)(q21;q21) to DLBCL and serve as a reminder of the risk of the progression of DLBCL with a distinct clonality immediately after H. pylori eradication for low-grade MALT lymphoma.

Mucosa-associated lymphoid tissue (MALT) lymphoma presentation in the oral cavity is very rare. Reported herein is a case of intraoral MALT lymphoma of the minor salivary gland in a 70-year-old woman with Sjogren's syndrome. Unexpectedly, a spontaneous clinically and histologically confirmed regression occurred 1 month after the tumor biopsy for diagnosis. Considering that salivary MALT lymphoma is associated with Sjogren's syndrome and that the chronic inflammation caused by Sjogren's syndrome persisted, it is hypothesized that the tumor clone might be present in the regressed lesion. Minimal residual tumor clone identical with the primary lesion was detected using the polymerase chain reaction (PCR) clonality assay for immunoglobulin heavy chain gene (IgH) rearrangement. No recurrence was clinically evident 38 months after the diagnosis. Spontaneous regression of MALT lymphoma should be examined at the molecular level in addition to clinical and histological evaluations. When minimal residual disease is detected, close follow up is necessary for early detection of the tumor relapse.

Thymic MALT lymphoma shows certain distinctive features among MALT lymphomas, such as expression of IgA isotype, consistent lack of API2-MALT1 gene fusion, and very strong association with autoimmune disease, especially Sjogren's syndrome. To help clarify the nature of the clonal lymphoid infiltrates, we analysed the usage and somatic hypermutation of the Ig heavy chain variable region (V(H)) genes in nine different cases. The V(H) rearrangement was potentially functional in all cases and was restricted to the V(H)3 family. V(H) usage was biased toward V(H)3-30 (five cases) and V(H)3-23 (three cases) segments, which have both been frequently expressed by autoimmune B cells. Somatic hypermutation was absent in five cases. Fewer than the expected replacement mutations were found in the framework regions in two cases, indicating a negative antigen selection pressure. Ongoing mutation was absent in all cases. D segment usage was varied, whereas J(H) segment usage was restricted to J(H)4. The observed patterns of V(H) usage and mutations suggested that specific antigens may play a pathologically relevant role in the genesis or progression of thymic MALT lymphoma.

p16/INK4a gene alterations have been associated with tumor progression in lymphoid malignancies. However, their significance in mucosa-associated lymphoid tissue (MALT) lymphoma is unclear. We investigated p16 gene methylation and mutation in a large series of untreated cases of pulmonary MALT lymphoma and diffuse large B-cell lymphoma (DLBL), and correlated p16 gene alterations with a MALT lymphoma-specific API2-MALT1 fusion and the clinicopathologic features of MALT lymphoma. The API2-MALT1 fusion was detected by multiplex reverse transcription polymerase chain reaction in 25/60 (42%) cases of MALT lymphoma, but none of 11 DLBLs. Methylation-sensitive single-strand conformation analysis showed that p16 gene methylation was frequently detected in 36/60 (60%) cases of MALT lymphoma. The gene was similarly methylated in DLBL cases (6/11, 55%). A p16 gene mutation was found in one (p16 gene-methylation) of 44 MALT lymphomas and in none of six diffuse large B-cell lymphomas. Statistical analysis showed that the p16 gene methylation status did not correlate with API2-MALT1 fusion or any of the clinicopathologic factors including serum LDH, clinical stage, and increased large cells. These findings suggest that p16 methylation is not associated with tumor progression, but may be an early event in MALT lymphomagenesis that might be maintained through the progression of the tumor.

Mucosa-associated lymphoid tissue (MALT) lymphoma constitutes up to 90% of primary pulmonary lymphomas, but its diagnosis is often difficult. API2-MALT1 fusion is specific to MALT lymphoma and is detected in nearly half of the pulmonary cases. Cytologic examinations have played a pivotal role in the diagnosis of pulmonary tumors; however, cytologic specimens have only infrequently been used for molecular studies. In this study, we performed a multiplex reverse transcription-polymerase chain reaction (RT-PCR) assay to detect the API2-MALT1 fusion transcript in archival cytologic specimens used as RNA sources. We studied 3 pulmonary MALT lymphoma cases that were positive for the fusion gene as detected with RNA extracted from diagnostic histologic specimens. In 1 case, a conventional PCR clonality assay for the immunoglobulin heavy chain gene rearrangement failed to detect the monoclonality. In all 3 cases, the fusion transcript was successfully detected in the cytologic specimens of sputum, bronchoalveolar lavage fluid, bone marrow smears, and pleural effusions. This finding suggests that such specimens can be used as RNA sources in multiplex RT-PCR assays for the API2-MALT1 fusion transcript. The detection of API2-MALT1 fusion as carried out with these specimens would be useful as an ancillary assay for the diagnosis, staging, and follow-up of pulmonary MALT lymphoma.

Gastric MALT lymphoma shows unique features including regression by Helicobacter pylori eradication and API2-MALT1 fusion. We performed a molecular and clinicopathologic study for 115 cases. All eradication-responsive cases were devoid of API2-MALT1 fusion. All tumors positive for the fusion and all negative for H. pylori infection were nonresponsive to the eradication. Consequently, gastric MALT lymphomas were divided into three groups: Eradication-responsive and fusion-negative (group A, n = 72), eradication-nonresponsive and fusion-negative (group B, n = 22), and eradication-nonresponsive and fusion-positive (group C, n = 21). Group A tumors were characterized by low clinical stage and superficial gastric wall involvement, and group C tumors by low H. pylori infection rate, advanced clinical stage, and nuclear BCL10 expression. All group C tumors showed exclusively low-grade histology. Group B tumors, which have not been well recognized, frequently showed nodal involvement, deep gastric wall involvement, and advanced clinical stage, and sometimes an increased large cell component. A multivariate discriminant analysis revealed that responsiveness to the eradication could be predicted accurately by negative API2-MALT1 fusion, positive H. pylori infection, low clinical stage, and superficial gastric wall invasion, the former being the most important factor for the prediction. This 3-group categorization may be helpful for a comprehensive understanding of gastric MALT lymphoma.

Background: Mucosa-associated lymphoid tissue (MALT) lymphoma involving multiple organs is not well characterized., Methods: To obtain a better understanding of gastric MALT lymphoma with multiple organ involvement, we compared Helicobacter pylori infection status; response to eradication therapy; prevalence of genetic abnormality, including t(11;18)(q21;q21); and clonality of tumor cells between patients with gastric MALT lymphoma with and without multiple organ involvement., Results: Of 54 patients with only gastric involvement, 51 were positive for H. pylori (94.4%), whereas only 3 of 9 patients with multiple organ involvement had the infection (33.3%). Among those who received eradication therapy, the remission rate in patients with only gastric involvement was significantly higher than that in patients with multiple organ involvement (71.4% vs 33.3%; P < 0.05). The positive rate of API2-MALT1 fusion transcripts was significantly greater in patients with multiple lesions with either single or multiple organ involvement than in those with a single gastric lesion (71.4% vs 12.5%; P < 0.05), but 2 of 2 patients with multiple gastric lesions had the fusion transcripts. Of 5 patients with multiple organ involvement tested for clonality of the CDR3 region, distinct clones were detected in lymphoma lesions in different organs in 3 patients, whereas the identical clone was present in the different lesions in the remaining 2 patients., Conclusions: Gastric MALT lymphoma with multiple organ involvement is often associated with API2-MALT1 fusion transcripts. Moreover, H. pylori infection is rare in patients with multiple organ involvement as compared to those with only gastric involvement. Patients with gastric MALT lymphoma with multiple organ involvement who are positive for H. pylori are resistant to eradication therapy.

The API2-MALT1 fusion gene was originally identified from a t(11;18)(q21;q21) translocation, a specific chromosomal abnormality that is found in mucosa-associated lymphoid tissue (MALT) lymphoma. Gastric MALT lymphomas positive for the API2-MALT1 fusion gene do not respond to Helicobacter pylori-eradication therapy, but otherwise, the incidence and clinicopathological behavior of colorectal MALT lymphoma with this genetic abnormality are unclear. We examined the API2-MALT1 fusion by multiplex RT-PCR method in 47 cases of MALT lymphoma and 13 cases of diffuse large B-cell lymphoma and evaluated the relevance of API2-MALT1 positivity to the clinical and pathological features. The mean ages of MALT lymphoma and diffuse large B-cell lymphoma patients were 65 (range, 37-87 y) and 58 (range, 14-85 y) years, respectively. API2-MALT1 fusion genes were detected in seven cases (15%) of MALT lymphoma and one case (8%) of diffuse large B-cell lymphoma. In MALT lymphomas, the tumor size in API2-MALT1-positive cases was 62 +/- 39 mm (mean +/- SD), statistically larger than that in API2-MALT1-negative cases (25 +/- 19 mm; P <.01). The API2-MALT1-positive cases demonstrated more advanced clinical stages and a male predominance, compared with API2-MALT1-negative cases. Thus, API2-MALT1-positive tumors should be cared for as a more aggressive subgroup and be followed for a longer time.

Cutaneous marginal zone B-cell lymphoma is a recently proposed entity and constitutes a cutaneous counterpart of extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT). Borrelia burgdorferi infection has been suggested as a possible causative agent in European cutaneous cases of marginal zone B-cell lymphoma, whereas API2-MALT1 fusion and BCL10 mutation are highly associated with MALT lymphoma. Aberrant nuclear BCL10 expression may be closely correlated with API2-MALT1 fusion in gastric and pulmonary MALT lymphomas. We examined 24 Asian cases of cutaneous marginal zone B-cell lymphoma for B. burgdorferi involvement, API2-MALT1 fusion, BCL10 cellular expression, and BCL10 mutation. Neither Borrelia DNA nor API2-MALT1 fusion transcript was detected. Nuclear BCL10 expression was evident in tumor cells of 11 of 24 cases, although BCL10 mutation was found in one case only. Clinicopathologically, nuclear BCL10 was more frequently expressed in macroscopically nodular lesions than in plaques or papules (p = 0.0031). These data suggest that 1) B. burgdorferi infection may not play an important role in developing cutaneous marginal zone B-cell lymphoma in Asian cases, 2) neither API2-MALT1 fusion nor BCL10 mutation is closely associated with the pathogenesis, 3) aberrant nuclear BCL10 may frequently be expressed in the absence of these genetic abnormalities, and 4) nuclear BCL10 expression may be clinically important because it was observed in locally aggressive tumors.

The chromosomal translocation t(11;18) is a unique chromosomal aberration associated with mucosa-associated lymphoid tissue lymphoma. API2 and MALT1 genes have been identified around this translocation. We attempted to find chromosomal abnormalities focusing mainly on the t(11;18) translocation in formalin-fixed, paraffin-embedded tissues of ocular adnexal lymphoproliferative disorders using multiplex reverse transcriptase-polymerase chain reaction and/or two-color interphase fluorescence in situ hybridization. By these methods, the t(11;18) translocation was detected in 1 of 8 patients with reactive lymphoid hyperplasia (13%), 3 of 23 with mucosa-associated lymphoid tissue lymphoma (13%), and 2 of 14 with diffuse large B-cell lymphoma with/without mucosa-associated lymphoid tissue lymphoma (14%). Moreover, we performed fluorescence in situ hybridization analysis to detect any numerical aberration of chromosomes 3, 7, 12, and 18 on some specimens nonselectively. No numerical chromosomal abnormalities were detected in 3 cases of reactive lymphoid hyperplasia, whereas three of four cases of mucosa-associated lymphoid tissue lymphoma and all four cases of diffuse large B-cell lymphoma with/without mucosa-associated lymphoid tissue lymphoma components exhibited one or more abnormalities. These findings indicate a possibility that at least in the ocular adnexa, some diffuse large B-cell lymphomas are derived from mucosa-associated lymphoid tissue lymphomas.

t(11;18)(q21;q21) is associated with mucosa-associated lymphoid tissue (MALT)-type lymphoma and results in API2-MALT1 fusion. However, its clinicopathologic significance remains unclarified. API2-MALT1 fusion is detected most frequently in MALT lymphomas primarily involving the lung. We therefore screened 51 cases of pulmonary MALT lymphoma for API2-MALT1 fusion, and studied its relationship with clinicopathologic factors including the immunohistochemical expression of BCL10, another MALT lymphoma-associated molecule. The API2-MALT1 fusion transcript was detected in 21 of 51 (41%) cases, and was correlated with the absence of any underlying autoimmune disease, and with a normal serum lactate dehydrogenase, a "typical" histology without marked plasmacytic differentiation or an increased number of large cells, and aberrant nuclear BCL10 expression. However, its prognostic impact was not identified in the limited follow-up (6 to 187 months, median 27). These data suggest that the API2-MALT1 fusion may be a causative gene abnormality unrelated to autoimmune disease. In addition, this alteration may define a homogeneous MALT lymphoma subtype that is clinically more indolent and histologically more "typical." Aberrant nuclear BCL10 expression may have a possible role as a tool to screen for this API2-MALT1 fusion. A large-scale study with a long follow-up is necessary to establish the prognostic significance of API2-MALT1 fusion.

Approximately 10% of gastric low-grade B-cell lymphomas of mucosa-associated lymphoid tissue (MALT) type are unresponsive to Helicobacter pylori ( H. pylori) eradication treatment, and many of them contain an API2-MALT1 chimeric transcript mediated by t(11;18)(q21;q21) translocation. We here review the current status on the interrelationship among clinical features, H. pylori infection status, responsiveness to antibacterial treatment, and API2-MALT1 chimeric transcript of gastric MALT lymphoma in a unicenter study experience and discuss the clinicopathologic significance of API2-MALT1 chimeric transcript in gastric MALT lymphoma. We enrolled 59 patients with gastric MALT lymphoma in a unicenter study. H. pylori infection status and clinical stages were investigated. Antibacterial treatment and subsequent follow-up endoscopy were performed for the assessment of responsiveness of MALT lymphoma in every patient. All cases were examined for API2-MALT1 chimeric transcript by means of RT-PCR and sequencing analyses using RNA extracted from tissues. H. pylori infection status was assessed as positive in 50 patients and negative in 9. Antibacterial treatment achieved complete or partial remission in 41 patients and no change in 12. API2-MALT1 chimeric transcript was detected in 9 patients, all of whom showed no change in response to treatment. Notably, responsiveness to H. pylori eradication treatment most clearly delineated the enrolled cases into two groups, indicating that six factors ( H. pylori infection, API2-MALT1 chimeric transcript, cobblestone mucosa and submucosal tumor in gross appearance, nodal involvement, and clinical stage) were statistically significant. On the other hand, comparison of two groups from the standpoint of H. pylori or API2-MALT1 chimeric transcript status revealed a lesser number of the statistically significant factors (two and three, respectively). Gastric MALT lymphoma characterized by unresponsiveness to antibacterial treatment contains all API2-MALT1 chimeric transcript-positive cases and may constitute a distinct group often seen with nodal involvement and an advanced clinical stage. This group is thought to be unrelated to H. pylori infection in its pathogenesis, and might share a unifying feature of genetic alteration such as involving the MALT1 locus on chromosome 18. Investigation in the future will clarify this issue and establish the clinical implication of such genetic alteration as the predictive factor for gastric MALT lymphoma.

We report a very rare case of primary low grade mucosa associated lymphoid tissue (MALT) lymphoma of the oesophagus. An 83 year old woman was referred to our hospital in June 1999 for further examination and treatment of oesophageal tumour. Although a physical examination and laboratory data showed no significant abnormalities, endoscopic observation revealed two slightly elevated submucosal tumour-like lesions of the oesophagus. Tissue specimens were obtained by endoscopic mucosal resection of the oesophagus using a cap fitted panendoscope. The lesions were composed of diffuse small atypical lymphoid cells--that is, centrocyte-like cells--which were stained with CD20, L26, BCL-2, and kappa, but not with CD3, CD5, CD10, or cyclin D1. Monoclonality was detected by polymerase chain reaction analysis using the primer for CDR-3 of immunoglobulin H and diagnosed as low grade MALT lymphoma of the oesophagus. The tumours were considered to be completely resected and therefore additional treatment was not administered. The patient is alive and well 22 months after treatment and diagnosis.

Extranodal marginal-zone B-cell lymphoma (MZBL) of mucosa-associated lymphoid tissue (MALT) arising in the thymus is rare, with the largest series in the literature including only three cases. In the present study, we investigated 15 cases of thymic MALT lymphoma to systematically characterize its clinical, histopathological, and molecular features. There was a marked female predilection (male:female = 1:4), with a mean age of 55 years at diagnosis. There was a strong association with autoimmune disease, especially Sjögren's syndrome. Histologically, the thymic lymphoma showed the characteristic morphological features of extranodal MZBL of MALT type. Cysts were common. Prominent lymphoepithelial lesions were formed by centrocyte-like cells infiltrating and expanding the Hassall's corpuscles and epithelium lining the cysts. Plasmacytic differentiation was apparent in all cases. Notably, 13 of 15 cases expressed immunoglobulin (Ig) A phenotype; IgA expression in thymic MALT lymphoma was in striking contrast with the IgM phenotype observed in most of the Sjögren's syndrome-associated MZBLs and MALT lymphomas at other sites. Epstein-Barr virus was absent, and API2-MALT1 gene fusion, a recently reported MALT lymphoma-specific gene abnormality, was not detected in any case. Although one patient died of disease 85 months after the diagnosis, other patients were alive with overall 3-year and 5-year survival rates being 89% and 83%, respectively. Among the 22 patients reported previously and in the present series, at least 17 patients (77%) were Asians. These data indicate that thymic MALT lymphoma may represent a distinct subgroup of MALT lymphoma characterized by apparent predilection for Asians, a strong association with autoimmune disease, frequent presence of cysts, consistent plasma cell differentiation, tumor cells expressing IgA phenotype, and consistent lack of API2-MALT1 gene fusion.

In this report we describe the pathological and radiological findings in a patient with primary ureteral MALT lymphoma. We suggest that it is useful for the differential diagnosis of ureter masses that some MALT lymphomas may show a low signal intensity on T2-weighted MR images.

Malignant lymphoma of mucosa-associated lymphoid tissue (MALT) type is a distinct clinicopathological disease entity in the category of extranodal marginal zone B-cell lymphoma. Recently, we and others have shown that the API2 gene on chromosome 11 and the MALT1 gene on chromosome 18 are fused as a result of t(11;18)(q21;q21) in MALT lymphomas. Here we report a detection assay that can be used for formalin-fixed, paraffin-embedded specimens. It consists of a multiplex one-tube reverse transcriptase-polymerase chain reaction (RT-PCR) followed by three parallel multiplex nested polymerase chain reactions. Eight variants of the fusion transcripts have been reported to date. When these variants were used as positive controls, all were successfully detected. The subsequent direct sequencing confirmed the results. Using this rapid and simple method, we could detect API2-MALT1 fusion transcripts in 5 of 15 (33%) archival cases of MALT lymphoma for a frequency comparable with those of RT-PCR assays using frozen materials. The lung was the preferential anatomical site of origin of MALT lymphomas harboring API2-MALT1 fusion. No fusion transcript was detected in any of 20 high-grade B-cell lymphomas. Our multiplex RT-PCR assay, which can be used for routinely-processed paraffin samples, should serve as a useful molecular tool for clarifying the clinicopathological significance of API2-MALT1 fusion in MALT lymphoma.