At a Glance

Marginal zone lymphomas of mucosa-associated lymphoid tissue MALTomas are low-grade small B cell lymphomas that occur in extranodal sites (i.e., the primary site is not lymph node or spleen). They usually occur in adults and are slightly more common in women. The most commonly affected organs are the stomach, intestine, ocular adnexae, salivary glands, lungs, skin, thyroid, and breast.

These lymphomas have a distinct association at each site with autoimmune disorders and certain infectious agents, as follows:

  • Stomach: chronic active gastritis and Helicobacter pylori infection

  • Small intestine: Campylobacter jejuni (infection and immunoproliferative small intestinal disease (IPSID), which occurs in the Middle East, South Africa, and other tropical and subtropical locations

  • Ocular adnexa: Chlamydia psittaci

  • Salivary gland: Sjogren syndrome

  • Lung: possible association with hepatitis C

  • Skin: Borrelia burgdorferi infection in Europe

  • Thyroid: Hashimoto thyroiditis

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

MALTomas are diagnosed by biopsy of the affected organ. The neoplastic infiltrate is composed of small B-cells with moderate clear cytoplasm (“monocytoid” features) and variable numbers of plasma cells. Many MALTomas have retained normal germinal centers, often colonized by neoplastic cells. Another common feature is the lymphoepithelial lesion, where lymphoma cells invade and destroy the epithelial cells of the affected organ. Pulmonary MALTomas have a classic “lymphangitic pattern” of spread.

Immunohistochemical staining of the biopsy can be helpful in highlighting the neoplastic B-cells, which are typically CD20+, CD5-, and CD10-. By definition, staining for cyclin D1 is negative. Helicobacter pylori infection in the stomach may also be highlighted by immunohistochemical or special staining.

Flow cytometry of fresh tissue can be helpful in identifying the monoclonal B-cell population and confirming its immunophenotype (usually CD5 negative, CD10 negative B-cells).

Molecular polymerase chain reaction (PCR) studies to look for IgH gene rearrangement may detect a clonal B cell population. Caution should be exercised, however, since MALTomas can have a negative result due to admixed normal germinal centers and benign proliferations, such as Hashimoto thyroiditis, can be clonal.

Cytogenetic karyotype and fluorescence in situ hybridization (FISH) studies can be helpful, but not all MALTomas have mutations detected. Chromosomal translocations that are common in MALT lymphomas include t(11;18) (q21;21), t(1;14) (p22;q32), t(14;18) (q32;q21), t(3;14) (p14.1q32), trisomy 3, and trisomy 18. Some are more common in specific sites: t(11;18) in lung and stomach; t(14;18) in orbit and salivary gland; and t(3;14) in the skin, thyroid, and orbit.

Patients with MALTomas may have additional testing for autoimmune disorders or infectious disease.

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications – OTC drugs or Herbals – that might affect the lab results?

MALToma can be difficult to diagnose, especially since it commonly occurs in patients with autoimmune diseases and it can have considerable histologic overlap with benign reactive chronic inflammation. MALTomas are usually indolent. Sometimes they recur in the same site or in a different extranodal site. Some MALTomas can be more aggressive, most commonly seen in gastric MALTomas which lack t(11;18) that can progress to diffuse large B-cell lymphoma.

Some MALTomas regress with treatment of the underlying infectious agent, especially gastric MALTomas with H. pylori infection. Interestingly, gastric MALToma with t(11;18) is known for its resistance to H. pylori infection treatment, although it does not progress to a higher grade diffuse large B-cell lymphoma.