Overall median age of presentation is 61 years.
The stomach is the most frequently involved organ, and in most cases (detected in 90%), there is a strong association between gastric MALT lymphoma and chronic Helicobacter pylori infection.
Other sites that may be involved include the salivary glands, eyes, lung, intestinal tract, skin, and thyroid gland. May also occur (rarely) in breasts, dura, and genitourinary tract. Autoimmune diseases have been linked to nongastric MALT lymphoma.
Diagnosis is based on history, physical exam, radiologic imaging studies, histopathologic and immunohistochemical evaluation of the biopsy specimen, and special molecular laboratory techniques.
Treatment is based on the histologic subtype and severity of symptoms at presentation. Surgery, radiation therapy, and chemotherapy all play a role. H pylori -eradication therapy is the mainstay of treatment for localized H pylori -positive gastric MALT lymphoma.
Generally regarded as indolent or low-grade lymphoma; however, high-grade histologic transformation can occur.
The World Health Organization (WHO) has defined MALT (mucosa-associated lymphoid tissue) lymphoma as "an extranodal lymphoma composed of morphologically heterogenous small B cells, including marginal zone cells, cells resembling monocytoid cells, small lymphocytes, and scattered immunoblasts and centroblast-like cells".  Plasma cell differentiation occurs in a proportion of cases. The infiltrate is located in the marginal zone of reactive B-cell follicles and extends into the interfollicular region. Lymphoepithelial lesions develop in epithelial tissues due to infiltration of the epithelium with neoplastic cells.  The stomach is the most commonly involved organ, and there is an important association with chronic Helicobacter pylori infection in the majority of gastric MALT lymphoma cases. MALT lymphomas are categorized as indolent or low-grade lymphomas. Very rarely do they show features of high-grade histology or transformation at the time of initial presentation.
Luton and Dunstable Hospital NHS Foundation Trust
RJ declares that he has no competing interests.
Royal Free Hospital
CM declares that he has no competing interests.
Professor of Medicine
Department of Internal Medicine I
Division of Oncology
Medical University Vienna
MR is an author of a number of references cited in this monograph.
Cleveland Clinic Taussig Cancer Center
AL declares that he has no competing interests.
Consultant Medical Oncologist
Royal Marsden Hospital
IC has been reimbursed by Roche Products, the manufacturer of rituximab, for attending several conferences. IC has also served on advisory boards and received honorarium for giving presentations for Roche Products. IC has received research funding from Novartis to conduct academic studies in the treatment of colorectal cancer.
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