MALT (mucosa-associated lymphoid tissue) lymphoma is a rare form of malignant non-Hodgkin lymphoma (see this term) that affects B cells and grows at the expense of lymphoid tissue associated with mucous membranes, but also occurs, more rarely, in lymph nodes.
It accounts for about 5% of non-Hodgkin lymphoma diagnosed annually. Annual incidence is estimated at about 1/313,000.
The disease mainly affects adults over 60 years of age (median age 65 years) with a slight female predominance. It is very rare in children. MALT lymphoma can develop in the gastrointestinal tract (especially in the stomach), lungs and glands (lacrimal, thyroid and breast). The main symptoms are nonspecific and include fatigue, fever, nausea, constipation, weight loss and anemia. Other symptoms depend on the affected organs: abdominal pain in cases with gastric involvement, recurrent respiratory infections in cases with pulmonary involvement and visual impairment in cases with lacrimal gland involvement. In general, patients do not have lymphadenopathy.
In most cases, MALT lymphoma is secondary to autoimmune disease or chronic infection. There is a well-established link between chronic Helicobacter pylori infection and gastric MALT lymphoma. In 40% of cases of gastric lymphoma associated with H. pylori infection and in 53% of cases of MALT lymphoma not associated with H. pylori infection, MALT lymphoma is associated with a translocation t(11;18)(q21;q21) leading to the fusion of two genes, BIRC3 and MALT1, implicated in apoptosis regulation.
Diagnosis is based on histology of the lesion, as in all lymphomas, a complete blood count and biochemical analysis. Endoscopic examination is required for gastrointestinal or pulmonary lymphoma. MRI and CT scanning are required to determine the stage of the disease. Bone marrow biopsy is also performed.
Differential diagnoses include B cell lymphomas, diffuse large B cell lymphomas, all other non-Hodgkin lymphomas (see these terms), and infection with H. pylori.
Management and treatment
In cases with localized gastric involvement that are due to H. pylori, antibiotic therapy often results in regression of the lymphoma. In other cases, chemotherapy (chlorambucil, cyclophosphamide, or fludarabine) is required. Radiotherapy may be considered in cases of conjunctival lymphomas and in recurrent cases of localized forms, particularly gastric forms. Conjunctival MALT lymphoma is treated with interferon alpha-2a.
These lymphomas evolve slowly. When the lymphoma is isolated, the 10yr-survival rate after treatment is around 75%.