Marginal zone lymphoma (MZL)
Causes and risk factors
Marginal zone lymphomas account for approximately 8% of all non-Hodgkin's lymphomas. The stomach is the organ most frequently involved. Other frequent sites are the ocular adnexa, salivary glands, lung, and thyroid gland. The disease most often affects females, and the average age of onset is about 60 years old.
The causes of these lymphomas are only partially known. For example, gastric MALT lymphoma, in most cases, is associated with Helicobacter pylori infection, and eradication of the bacterium by targeted antibiotic therapy can also lead to cure of the lymphoma itself. For the other MALT lymphomas, there is not such a clear association with bacterial infections; only recently, thanks to the contribution of the San Raffaele Scientific Institute, the association between lymphomas of the ocular adnexa and the infection of the bacterium Chlamydia psittaci has been discovered. Finally, hepatitis C virus has been associated with the development of marginal zone lymphomas particularly for those with onset in the spleen.
Which are the symptoms?
Marginal zone lymphomas manifest themselves differently, depending on the site of onset. For example, lymphomas of the stomach may lead to digestive disorders; lymphomas of the ocular adnexa may manifest with the appearance of eyelid swelling or visual changes of various kinds; lymphomas of the spleen may be associated with spleen enlargemen. Often, however, the disease may remain silent for a long time, and the diagnosis may be incidental (during examinations performed for other reasons).
How is it diagnosed?
To obtain a definite diagnosis of marginal zone lymphoma, it is essential to biopsy the suspected site (e.g., gastric biopsies during a gastroscopy). Very often, after the diagnosis, the patient is asked to perform additional tests (for example, blood tests including blood count, CT or MRI of certain body areas, endoscopic examinations, bone marrow biopsy) in order to define the exact extent of the disease, exclude any other sites involved and set up an appropriate therapy.
How is it treated?
Treatment of marginal zone lymphomas is highly variable depending on the site, extent, and rate of growth of the disease. For example, gastric MALT lymphoma associated with Helicobacter pylori infection is first treated with a combination of antibiotics and drugs that protect the gastric mucosa by reducing its acid secretions. Generally, the disappearance of Helicobacter pylori infection is associated with a slow, but steady, regression of the disease. With regard to marginal zone lymphomas involving organs other than the stomach or relapsed gastric lymphomas, treatment may involve the use of chemotherapy drugs (in tablets or by intravenous infusion) and/or radiation (radiotherapy). In selected cases, surgical approach may be useful, while in some forms (e.g., those associated with hepatitis C virus infection) an antiviral therapy may be undertaken with regression of the lymphoma. The prognosis is generally good, since it is possible to obtain healing or at least an appreciable slowing of the course of the disease.