Marginal zone lymphoma - MALT lymphoma.

Marginal zone lymphomas come in three types. In the past I have written about splenic marginal zone lymphoma (SMZL) also known as splenic lymphoma with villous lymphocytes (SLVL) and I shall say nothing more about that today.

The best known of the marginal zone lymphomas are those occurring in the extranodal mucosa associated lymphoid tissue, the so-called MALT lymphomas. The tumors are morphologically heterogeneous being composed of small centrocytes, monocytoid cells, small round cells and scattered immunoblasts and centroblasts. A proportion of cases show differentiation into plasma cells.

Malt lymphomas comprise 7-8% of B cell lymphomas and about half of gastric lymphomas. Median age of presentation is 61 and there is a slight female preponderance. The association with Helicobacter pylori is well known for gastric lymphomas and there is a similar relationship with Chlamidia psittaci for ocular adenexal Malt lymphoma and with Borrelia burgdorferi (the Lyme disease agent) for cutaneous Malts. There is a rare form of MALT lymphoma which makes immunoglobulin alpha chains and which was once known as alpha heavy chain disease, but is now called immunoproliferative small intestinal disease (IPSID) and which occurs in the middle east and the Cape area of South Africa. This type of MALT is associated with Campylerbacter jejuni. Thyroid and salivary gland MALTs are known to be often preceded by autoimmune processes in the respective glands.

Sites of MALTs are nearly 50% in the gastrointestinal tract, head and neck 14%, lung 14%, eyes 12%, skin 11%, thyroid 4% and breast 4%. Most patients have localised disease with less than 20% showing bone marrow involvement. Involvement of both of paired organs is common. A third of patients have a paraprotein.

The immunophenotype is CD19+, CD20+, CD79a+, CD5-, CD23-, CD10-, CD21+ and CD35+, but there is no specific marker for MALT lymphoma. Chromosomal abnormalities include t(11;18)(q22;q32) in pulmonary and gastric tumors, t(14;18)(q31;q21) in ocular and salivary gland tumors and t(3;14)(p14.1;q32) in ocular, thyroid and skin tumors. Also commonly seen are trisomy 3 and trisomy 18, but these are non-specific.

These tumors are usually indolent and may respond to treatment with appropriate antibiotics. They also tend to be sensitive to radiotherapy.