Extranodal Marginal Zone B-cell Lymphoma (MALT Lymphoma)

Extranodal Marginal Zone B-cell Lymphoma (MALT Lymphoma)

Pei Lin, MD

MALT lymphoma involving small intestine. The neoplastic infiltrate is diffuse. A few residual germinal centers image are present. The villi are blunted.

MALT lymphoma involving small intestine. The neoplastic cells are predominantly small, and many cells have pale, monocytoid cytoplasm.



  • Extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma)


  • Low-grade B-cell lymphoma of MALT

  • MALToma


  • Low-grade B-cell lymphoma arising at extranodal sites, presumably in marginal zone of reactive follicles


Infectious Agents

  • Implicated in pathogenesis of MALT lymphomas

    • Helicobacter pylori

      • Gastric marginal zone lymphoma

    • Campylobacter jejuni

      • Immunoproliferative small intestinal disease; also known as α heavy chain disease

    • Chlamydia psittaci

      • Ocular adnexal marginal zone lymphoma

    • Borrelia burgdorferi

      • Cutaneous marginal zone lymphoma

      • More common in Europe

Autoimmune Disorders

  • 2 autoimmune diseases have been implicated in pathogenesis of MALT lymphomas

    • Sjögren syndrome

      • MALT lymphomas of parotid gland and lung

    • Hashimoto thyroiditis

      • Thyroid MALT lymphoma

Chromosomal Translocations

  • Identified in 30-40% of MALT lymphomas

  • Result in NF-κB pathway activation resulting in enhanced cell survival and proliferation and impaired apoptosis

MALT Lymphomas Without Chromosomal Translocations

  • Possible role for antigen drive

    • Chronic antigen stimulation via infection or autoimmune disease

      • Leads to accumulation of extranodal lymphoid tissue

      • Polyclonal B-cell population evolves to oligoclonal and then monoclonal B-cell population

  • No central role for NF-κB activation



  • Incidence

    • 7-8% of all B-cell non-Hodgkin lymphomas

  • Age

    • Median: 61 years

  • Gender

    • Female predominance


  • Subset of patients are asymptomatic

  • Symptoms are related to organ involved

    • Stomach: Anemia, weight loss, and pain are common

    • Lung: ± cough and dyspnea

    • Mass and related symptoms in other locations


  • Stomach MALT lymphoma: Antibiotics to eradicate H. pylori

    • Chemotherapy ± radiation if transformed to large B-cell lymphoma or disseminated

  • Ocular adnexa

    • MALT lymphoma often stage IE and is treated by radiation alone

  • Other sites

    • Chemotherapy &/or radiation therapy depending on

      • Site, size, and stage


  • Stomach MALT lymphoma

    • Lymphoma can regress after eradication of H. pylori by antibiotics; true in ˜ 75% of cases

    • t(11;18)(q21;q21) is associated with resistance to antibiotics

    • < 10% of cases transform to diffuse large B-cell lymphoma

    • 5-year overall survival is ˜ 90%

    • 25-35% relapse rate in stomach or other extranodal sites

  • Other sites of MALT lymphoma

    • Disseminated disease is more common

    • Higher relapse rate


Radiographic Findings

  • Single or multiple masses

  • Lung(s) involved by MALT lymphoma ± consolidation

Endoscopic Findings

  • Gastric or intestinal MALT lymphoma: ± mass, ulcer, or bleeding


Histologic Features

  • Diffuse or nodular pattern of growth

  • Expansion of marginal zone by cytologically heterogeneous cell population

    • Predominantly centrocyte-like cells with small irregular nuclei

    • Monocytoid appearance with distinct rim of clear cytoplasm

    • Scattered large cells (centroblasts or immunoblasts) are present; up to 10% of all cells

    • ± plasmacytoid differentiation; ± Dutcher bodies

  • Hyperplastic lymphoid follicles are common

    • ± colonized by lymphoma imparting nodular pattern

  • Lymphoepithelial lesions are common in epithelial tissues involved by MALT lymphoma

    • Infiltration and distortion of epithelial structures by 3 or more neoplastic lymphoid cells

    • Epithelial degeneration and glandular structure destruction

    • Most prominent in thyroid and parotid glands

  • Transformation to diffuse large B-cell lymphoma

    • Large cells form sheets or large clusters of > 20 cells

    • May coexist with MALT lymphoma at initial presentation

  • Multifocal disease

    • ˜ 25% of patients have > 1 extranodal site of involvement

Cytologic Features

  • FNA smears show polymorphous cell population

    • Small round or irregular lymphocytes, variable numbers of large cells &/or plasma cells

Lymph Nodes

  • Involvement is indistinguishable from nodal marginal zone B-cell lymphoma

    • Usually lymph nodes draining primary site of disease are involved

    • Distant lymph nodes involved in < 10% of patients

Bone Marrow

  • 10-20% of patients with MALT lymphoma have bone marrow disease at staging

  • Paratrabecular &/or nonparatrabecular aggregates

    • Follicular dendritic cells commonly present in aggregates

  • Sinusoidal pattern highly unusual


  • Most common B-cell lymphoma of skin

  • Follicular colonization can be prominent; these lesions closely mimic follicular lymphoma

Ocular Adnexal Region

  • Includes orbital soft tissue, conjunctiva, and lacrimal gland

  • MALT is most common type of lymphoma at this location


  • Lymphoepithelial lesions common in MALT lymphoma and lymphocytic interstitial pneumonitis

  • Circumscribed mass supports diagnosis of MALT lymphoma

Salivary Gland

  • Arises in background of myoepithelial sialadenitis (MESA)

  • Lymphoepithelial lesions (epithelial-myoepithelial islands) common in MALT lymphoma and MESA

  • Concentric zones of pale cells around ducts are helpful clue for MALT lymphoma

Thyroid Gland

  • Arises in background of Hashimoto thyroiditis

  • Lymphoepithelial lesions common in both MALT lymphoma and Hashimoto thyroiditis

  • Lymphoma cells within follicles tend to be centrocyte-like cells

  • Lymphoma cells outside follicles often are extremely plasmacytic


  • Lymphoepithelial lesions are uncommon at this site

  • Can arise in or be disseminated to breast

Other MALT Lymphoma Sites

  • Very wide range of body sites can be involved

    • Dura, soft tissues, thymus, gallbladder, kidney, bladder



  • CD19(+), CD20(+), CD22(+), CD79a(+), pax-5(+)

  • IgM(+) > IgA(+) > IgG(+)

  • Monotypic Ig light chain(+); best seen in plasmacytoid cells

  • Bcl-2(+), CD43(+/-), Bcl-10(+/-)

  • Ki-67(MIB-1) is low; high in residual reactive germinal centers

  • IgD(-) but demonstrates intact follicular IgD(+) mantle zones

  • CD21 highlights follicular dendritic cell (FDC) meshworks in follicles

    • Meshworks are disrupted by follicular colonization

  • Cytokeratin(-); useful for highlighting lymphoepithelial lesions

  • CD10(-), Bcl-6(-), Cyclin-D1(-)

  • T-cell antigens(-), EBV-LMP1(-)

Flow Cytometry

  • Monotypic surface Ig light chain(+)

  • FMC7(+), CD11c(+/-), CD23(-/+), CD25(-), CD103(-)


Jul 8, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Extranodal Marginal Zone B-cell Lymphoma (MALT Lymphoma)

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