MALT lymphoma

MALT lymphoma (MALToma) is a form of lymphoma involving the mucosa-associated lymphoid tissue (MALT), frequently of the stomach, but virtually any mucosal site can be afflicted. It is a cancer originating from B cells in the marginal zone of the MALT, and is also called extranodal marginal zone B cell lymphoma.

Associations
Gastric MALT lymphoma is frequently associated (72-98%) with chronic inflammation as a result of the presence of Helicobacter pylori.

The initial diagnosis is made by biopsy of suspicious lesions on esophagogastroduodenoscopy (EGD, upper endoscopy). Simultaneous tests for H. pylori are also done to detect the presence of this microbe.

In other sites, chronic immune stimulation is also suspected in the pathogenesis (e.g. association between chronic autoimmune diseases such as Sjögren's syndrome and Hashimoto's thyroiditis, and MALT lymphoma of the salivary gland and the thyroid).

Treatment
If the disease is limited to the stomach (which is assessed with computed tomography), then 70-80% of patients will have a complete regression on treatment with antibiotic eradication of H. pylori.

Others may be effectively controlled with the use of radiotherapy, or surgery. Both modalities may be curative in localized disease.

In contrast, if the disease has spread or has been refractory on antibiotics, chemotherapy may need to be considered.

A t(11;18)(q21;q21) chromosomal translocation, giving rise to a API2-MLT fusion gene, is predictive of poor response to eradication therapy.

Two other genetic alterations are known:
 * t(1;14)(p22;q32) which deregulates BCL10, at the locus 1p22.
 * t(14;18)(q32;q21), which deregulates MALT1, at the locus 18q21.

These seem to turn-on the same pathway as API2-MLT (i.e., that of NF-κB). They both act upon IGH, which is at the locus 14q32.

Epidemiology
Of all cancers involving the same class of blood cell, 8% of cases are MALT lymphomas.