Guidelines on Diagnosis and Treatment of Malignant Lymphomas

Extra-nodal Marginal Zone B-Cell
Lymphoma (Malt-Lymphoma)
Definition and Incidence
Extranodal Marginal Zone B-cell Lymphoma of Mucosa
Associated Lymphoid Tissue (MALT Lymphoma) is an extranodal
lymphoma consisting of heterogeneous small B-cells. The
gastrointestinal tract is the commonest site of development of
MALT lymphoma, and the stomach is the most common location
(85%). Gastric MALT lymphoma is considered to be derived from
MALT acquired as a result of Helicobacter pylori infection. The
incidence is 0.6 new cases / 100,000 population per year, median
age 60 years and sex ratio shows a slight female excess.
ICD-O Code 9699/3
Clinical Presentation
Most patients have a history of chronic inflammation, secondary
to autoimmune disorders or low grade infections which result in
accumulation of extranodal lymphoid tissue. Examples include
Helicobacter pylori associated chronic gastritis, Sjogren’s
Syndrome or Hashimoto’s thyroiditis. Helicobacter pylori is
detectable in most cases of gastric MALT lymphoma. Patients
with Sjogren’s syndrome and lymphoepithelioid sialadenitis have
a 40-fold increased risk of developing lymphoma, and most of
these are MALT lymphomas. Patients with Hashimoto’s thyroiditis
have a 3-fold increased risk of lymphoma development. Most
patients present with Stage I or II disease, but 20% of patients
have bone marrow involvement. Multiple extranodal sites are
present in 10% of patients at presentation, with 30% becoming
disseminated over time, and some transforming to DLBCL.
The 5-years overall survival is >80%.
Pathology and Genetics
The lymphoma cells infiltrate around reactive B-cell follicles,
external to a preserved follicle mantle, in a marginal zone
distribution, and spread out to form larger confluent areas
which eventually overrun some or most of the follicles. The
characteristic marginal zone B cells have small to medium sized,
slightly irregular nuclei with moderately dispersed chromatin
and inconspicuous nuclei, resembling those of centrocytes with
relatively abundant, pale cytoplasm. Plasmacytic differentiation is
present in approximately one-third of gastric MALT-type
lymphomas. Lymphoepithelioid lesions are usually present.
Phenotype:
CD19+ CD20+ CD22+ CD79a+ Slg+ Cd11c± CD43± CD5-
CD10- CD23-. The tumour cells typically express IgM, and less
often IgA or IgG, and show light chain restriction.
Genetics:
Trisomy 3 is found in 60% of cases, and the t(11,18)(q21;q21)
in 25-50% and is not found in other lymphomas.
Staging
As for other indolent lymphomas
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