HOMO SAPIENS DISEASES - MARGINAL ZONE LYMPHOMAS (MZL) OF THE MUCOSA-ASSOCIATED LYMPHOID TISSUE (MALT)-TYPE LYMPHOMAS (MALTOMAS)

Table of contents :


  • Aetiology
  • Pathogenesis
  • Localizations
  • Therapy
  • Prognosis
  • Web resources

  • Aetiology : the interaction of bacterial or viral antigens with host T-cells and antigen-presenting cells leads to a complex cascade resulting in clonal B-cell or plasma cell expansion. Although all immune responses are in effect clonal, MALT lymphomas are the result of immune responses gone awryref, in which persistence of the antigen leads eventually to an autonomous clonal proliferation. The pathogenesis of malignant lymphoma is a multi-step process that recapitulates many aspects of the normal immune response and of normal lymphocyte development. The patterns of spread of lymphomas reflect the homing patterns of normal lymphocytes, both microscopically, within lymph nodes, and macroscopically, at a clinical level. Thus, the site of presentation provides insight into the cellular origin of the neoplastic process. MALT lymphomas are primarily extranodal in distribution, retaining the phenotypic and functional properties of the mucosa-associated lymphoid system. Thus, MALT lymphomas are post-germinal center–derived B-cell lymphomas that arise in and home to mucosa-associated sites that have acquired lymphoid tissue as a consequence of a chronic inflammatory processref. Although MALT lymphomas arising in different organ systems share many pathologic and clinical similarities, there are also important differences. A successful immune response requires a delicate balance among antigen drive, lymphocyte proliferation, and lymphocyte apoptosis. In MALT lymphomas, unchecked proliferation of autoreactive B-cells can lead to both autoimmune disease, e.g., Sjogren’s syndrome or Hashimoto’s disease, and lymphomaref. In a parallel fashion, defective immunoregulation of responding T cells following chronic EBV infection may result in a cytokine storm, leading to a hemophagocytic syndrome and, rarely, to T-cell lymphomasref. In the above examples of lymphoma pathogenesis, defective immunoregulation characterized by either excess lymphocyte activation and proliferation or defective apoptosis leads ultimately to clonal expansion and lymphoma. An unanswered question is how chronic antigenic stimulation in the presence of H. pylori or C. psittaci infection leads not only to chronic B-cell proliferation but also to the specific translocations that characterize most MALT lymphomasref. In 2005 Bende et al. analyzed the structure of antigen receptors of a comprehensive panel of mature B non-Hodgkin's lymphomas (B-NHLs) by comparing, at the amino acid level, their immunoglobulin (Ig)VH-CDR3s with CDR3 sequences present in GenBank. Follicular lymphomas, diffuse large B cell lymphomas, Burkitt's lymphomas, and myelomas expressed a CDR3 repertoire comparable to that of normal B cells. Mantle cell lymphomas and B cell chronic lymphocytic leukemias (B-CLLs) expressed clearly restricted albeit different CDR3 repertoires. Lymphomas of mucosa-associated lymphoid tissues (MALTs) were unique as 8 out of 45 (18%) of gastric- and 13 out of 32 (41%) of salivary gland-MALT lymphomas expressed B cell antigen receptors with strong CDR3 homology to rheumatoid factors (RFs). Of note, the RF-CDR3 homology without exception included N-region–encoded residues in the hypermutated IgVH genes, indicating that they were stringently selected for reactivity with auto-IgG. By in vitro binding studies with 10 MALT lymphoma–derived antibodies, we showed that 7 of these cases, of which 4 with RF-CDR3 homology, indeed possessed strong RF reactivity. Of one MALT lymphoma, functional proof for selection of subclones with high RF affinity was obtained. Interestingly, RF-CDR3 homology and t(11;18) appeared to be mutually exclusive features and RF-CDR3 homology was not encountered in any of the 19 pulmonary MALT lymphomas studiedref. In HIV+ patients, MALT lymphoma is most commonly described in children. In an original case of HIV+ MALT lymphoma with bronchial, conjuctival and laryngeal involvement clinical and histopathological remission has been obtained with HAART aloneref.
    Pathogenesis :

    Characteristically the tumor-infiltrating T cells found in large numbers in MALT-type lymphomas are predominantly of CD4+ phenotype and may have impact on tumor pathogenesis (CXCR3 and its ligand CXCL9)
    Localizations: Kinds : Therapy : Prognosis : the International Extranodal Lymphoma Study Group (IELSG) study of non-gastric MALT lymphomas: Kaplan-Meier estimate of overall survival according to the International Prognostic Index risk groups (defined considering age, Ann Arbor stage, LDH levels, number of extranodal sites and performance status)


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