BCL10 in malignant lymphomas--an evaluation using fluorescence in situ hybridization

Recent Advances in the Genetic of MALT Lymphomas

Simple Summary

Mucosa-associated lymphoid tissue (MALT) lymphoma is the most common subtype of marginal zone lymphomas. These B-cell neoplasms may arise from many organs and usually have an indolent behavior. Recurrent chromosomal translocations and cytogenetic alterations are well characterized, some of them being associated to specific sites. Through next-generation sequencing technologies, the mutational landscape of MALT lymphomas has been explored and available data to date show that there are considerable variations in the incidence and spectrum of mutations among MALT lymphoma of different sites. Interestingly, most of these mutations affect several common pathways and some of them are potentially targetable. Gene expression profile and epigenetic studies have also added new information, potentially useful for diagnosis and treatment. This article provides a comprehensive review of the genetic landscape in MALT lymphomas.

Abstract

Mucosa-associated lymphoid tissue (MALT) lymphomas are a diverse group of lymphoid neoplasms with B-cell origin, occurring in adult patients and usually having an indolent clinical behavior. These lymphomas may arise in different anatomic locations, sharing many clinicopathological characteristics, but also having substantial variances in the aetiology and genetic alterations. Chromosomal translocations are recurrent in MALT lymphomas with different prevalence among different sites, being the 4 most common: t(11;18)(q21;q21), t(1;14)(p22;q32), t(14;18)(q32;q21), and t(3;14)(p14.1;q32). Several chromosomal numerical abnormalities have also been described, but probably represent secondary genetic events. The mutational landscape of MALT lymphomas is wide, and the most frequent mutations are: TNFAIP3, CREBBP, KMT2C, TET2, SPEN, KMT2D, LRP1B, PRDM1, EP300, TNFRSF14, NOTCH1/NOTCH2, and B2M, but many other genes may be involved. Similar to chromosomal translocations, certain mutations are enriched in specific lymphoma types. In the same line, variation in immunoglobulin gene usage is recognized among MALT lymphoma of different anatomic locations. In the last decade, several studies have analyzed the role of microRNA, transcriptomics and epigenetic alterations, further improving our knowledge about the pathogenic mechanisms in MALT lymphoma development. All these advances open the possibility of targeted directed treatment and push forward the concept of precision medicine in MALT lymphomas.

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.

Nuclear BCL-10 expression is common in lymphoplasmacytic lymphoma/Waldenström macroglobulinemia and does not correlate with p65 NF-kappaB activation

B-cell lymphoma 10 (BCL-10) is expressed in the cytoplasm of normal germinal center and marginal zone B-cells and is involved in lymphocyte development and activation. Aberrant nuclear expression of BCL-10 occurs in a subset of extranodal marginal zone B-cell lymphomas (MALT lymphomas), primarily those with the t(1;14)(p22;q32) or t(11;18)(q21;q21). Little is known about BCL-10 expression in lymphoplasmacytic lymphoma/Waldenström macroglobulinemia (LPL/WM). We assessed for BCL-10 in 51 bone marrow (BM) specimens involved by LPL/WM using immunohistochemical methods. All patients had monoclonal IgM in serum. Extent of BM involvement was assessed using PAX-5/BSAP and CD20 immunostains and the pattern and percentage of B-cells positive for BCL-10 was determined. The p65 subunit of nuclear factor-kappa B (NF-kappaB), a molecule downstream of BCL-10, was also assessed immunohistochemically. Nuclear BCL-10 staining was present in 28/51 (55%) specimens. BCL-10 expression correlated with greater extent of BM involvement (P=0.001), but did not correlate with serum IgM paraprotein levels, type of immunoglobulin light chain, or clinical variables. Nuclear expression of the p65 subunit of NF-kappaB was detected in 17/50 (34%) specimens, suggesting that NF-kappaB is active in a subset of LPL/WM. p65 NF-kappaB activation did not correlate with nuclear BCL-10 immunostaining. Cytogenetic analysis in 29 cases showed no evidence of the t(1;14) or t(11;18). These results indicate that nuclear BCL-10 expression is common in LPL/WM and does not correlate with MALT lymphoma-associated translocations or p65 NF-kappaB nuclear staining.

Contribution of Immunohistochemistry to Small B-Cell Lymphoma Classification

Although the small B-cell lymphomas show major morphologic overlapping, they have been recently shown to be distinct entities with several biologic and clinical differences. Therefore, the utility of a panel of paraffin-reactive antibodies in differentiating these neoplasms was investigated. Using clinical data and morphologic criteria, 134 cases of small B-cell lymphomas were grouped as those with (1) one strongly suggested diagnosis, (2) differential diagnosis between two types of lymphomas, and (3) small B-cell lymphoma without hints for further subclassification. With a panel of antibodies including CD5, CD10, CD23, CD43, bcl-2, and cyclin D1, most but not all cases could be precisely categorized. This panel confirmed the diagnosis in 96.5% of the cases from group 1. In group 2 it confirmed one of the two diagnoses in 81.5% of the cases. In group 3 it established a definitive diagnosis in 55% of the cases. When all groups were considered, a correct diagnosis could be established for 88.1% of cases; for 6.7% of them the authors remained with two possible diagnosis, and the broad "small B-cell lymphoma" was the only diagnosis for 5.2% of cases. CD10 separated most follicular lymphomas from other small B-cell lymphoid neoplasms. CD23 separated small lymphocytic lymphoma/chronic lymphocytic leukemia. Cyclin D1 separated mantle cell lymphoma. The present study selected CD10, CD23, and cyclin D1 as a minimal panel for the classification of small B-cell lymphomas, yielding a final diagnosis in 88.1% of the cases.

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.

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.