The marginal zone lymphomas (MZLs) are derived from memory-type or antigen-experienced B cells that reside in regions contiguous to the outer part of the mantle zones of B-cell follicles.
The World Health Organization (WHO) defines three separate MZL entities, namely, the extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (currently known as MALT lymphoma), the nodal marginal zone B-cell lymphoma (previously termed monocytoid lymphoma), and the splenic marginal zone B-cell lymphoma (with or without circulating villous lymphocytes).
Gastric MALT lymphoma is one of the best examples of a microbiologic (Helicobacter pylori) cause of a human malignancy.
MALT lymphomas arise from mucosa-associated lymphoid tissues in the context of chronic inflammation.
In addition to H pylori, other bacteria are possibly implicated in the pathogenesis of MZLs arising in the skin (Borrelia burgdorferi), in the ocular adnexa (Chlamydophila psittaci), and in the small intestine (Campylobacter jejuni).
Hepatitis C virus (HCV) appears involved in the pathogenesis of splenic MZL through antigen-driven stimulation of the lymphoma clone.
There is, however, a great geographic variation in the strength of these associations, which is not satisfactorily explained.
An increased risk of developing MALT lymphoma has been also reported in individuals affected by autoimmune disorders, especially Sjögren syndrome and systemic lupus erythematosus.
Several recurrent chromosomal translocations have been described in extranodal MZLs. Three of them—[t(11;18)(q21;q21), t(1;14)(p22;q32), and t(14;18)(q32;q21)]—are the best characterized; they each affect the same signaling pathway, activating nuclear factor-kappa B (NF-κB), a transcription factor that plays a major role in immunity, inflammation, and apoptosis (Table 63–1).
TABLE 63–1COMMON GENETIC LESIONS IN MUCOSA-ASSOCIATED LYMPHOID TISSUE LYMPHOMA |Favorite Table|Download (.pdf) TABLE 63–1 COMMON GENETIC LESIONS IN MUCOSA-ASSOCIATED LYMPHOID TISSUE LYMPHOMA
| ||Lesion ||Genes ||Frequency ||Sites |
|Translocations || |
Lung, skin, ocular adnexa, salivary gland
|Gains || |
| || |
No differences in sites
No differences in sites
|Losses ||–6q23 ||TNFAIP3 ||15%–30% ||No differences in sites |
EXTRANODAL MARGINAL ZONE LYMPHOMAS
The most common site of MALT lymphoma is the stomach, representing at least one-third of all cases.
Extranodal MZLs may also arise at many other sites, including the salivary gland, the thyroid, the upper airways, the lung, the ocular adnexa (lacrimal gland, conjunctiva, eyelid, orbital soft tissue), the breast, the liver, the urogenital system, the skin and other soft tissues, and even the dura.
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