Mucosa-associated lymphoid tissue (MALT) lymphomas
Mucosa-associated lymphoid tissue (MALT) lymphomas are a subtype of non-Hodgkin lymphoma that primarily affect the mucosa-associated lymphoid tissue found in various organs, notably the stomach and gastrointestinal tract. Often associated with chronic infections, especially Helicobacter pylori, MALT lymphomas are typically B-cell cancers originating from the marginal zone of the MALT. While they are relatively rare, these lymphomas are more common in individuals over the age of sixty and show a slightly higher prevalence in women. Symptoms can vary depending on the site of involvement, with gastric cases potentially causing indigestion, weight loss, and fatigue, while other sites may present different symptoms such as respiratory issues or vision problems.
Diagnosis is usually conducted through upper endoscopy and biopsy, with staging playing a critical role in determining treatment options. Many cases can be effectively treated with antibiotics to eradicate H. pylori, leading to remission in a significant number of patients. For those whose lymphoma does not respond to antibiotics or has spread, alternative therapies, including chemotherapy and radiotherapy, may be necessary. While some MALT lymphomas can be slow-growing and asymptomatic, regular monitoring is essential to detect any changes. Understanding the nature of MALT lymphomas, their associated risks, and treatment options is crucial for effective management and improved patient outcomes.
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Mucosa-associated lymphoid tissue (MALT) lymphomas
ALSO KNOWN AS: Extranodal lymphoma, MALT lymphomas, MALTomas
RELATED CONDITIONS: Indolent non-Hodgkin lymphoma (NHL), marginal zone B-cell lymphomas
DEFINITION: Mucosa-associated lymphoid tissue (MALT) lymphomas are a form of non-Hodgkin lymphoma frequently involving the MALT of the stomach and the gastrointestinal tract, usually as a result of Helicobacter pylori (H. pylori) infection. They are solid tumors that originate from B cells in the marginal zone of the MALT.
Risk factors: Around 90 percent of gastric MALT lymphoma cases are associated with H. pylori. On the skin, MALT lymphoma is likely associated with Borrelia burgdorferi infection, and Sjogren’s syndrome, an autoimmune disorder, is linked to salivary gland MALT lymphoma. In general, the incidence of non-Hodgkin lymphoma is two to three times higher among individuals with relatives who developed non-Hodgkin lymphoma, indicating familial clusters. In addition, a compromised immune system is a major risk factor for non-Hodgkin lymphoma development.
Etiology and the disease process: MALT lymphoma starts in mucosa-associated lymphoid tissue, which is lymphatic tissue, such as the stomach, thyroid gland, and lungs. Virtually any mucosal site can be afflicted; however, involvement of MALT lymphoma is rare. MALT lymphoma is a cancer of the B-cell lymphocytes. It belongs to the group of marginal zone B-cell lymphomas. can be either nodal or extranodal. In particular, MALT lymphoma is an extranodal marginal zone B-cell lymphoma.
Incidence: MALT lymphoma is a relatively rare form of non-Hodgkin lymphoma. In most cases, approximately two out of three, of MALT lymphoma affecting the stomach are caused by infection with H. pylori. The disease is more common in people over sixty, but it may occur at any age. MALT lymphoma is slightly more common in women than in men. Ethnicity may play a role in geographic differences among non-Hodgkin lymphoma incidence rates. In particular, gastric lymphomas have the highest recorded incidence in northern Italy.
Symptoms: The most common symptoms experienced by those with MALT lymphomas range from no symptoms to occult or gross gastrointestinal symptoms. Regardless of organ of origin, all MALT lymphomas appear to have similar clinical, pathological, and molecular features.
The symptoms exhibited depend on the site for MALT lymphoma. MALT lymphoma in the stomach may cause indigestion, bleeding into the stomach, weight loss, loss of appetite, and tiredness. Near the eyes, symptoms include redness, droopy eyelids, dark pink lumps, bulging eyes, and double vision. MALT causes coughing, chest pain, and shortness of breath in the lungs.
Screening and diagnosis: The initial diagnosis of MALT lymphoma is typically made by esophagogastroduodenoscopy (EGD), or upper endoscopy, which is a flexible tube passed down the gullet and into the stomach. Endoscopy is used to obtain photographs of the stomach, and a small sample of cells is extracted for assessment (biopsy). Tests for H. pylori are also common when gastrointestinal MALT lymphomas are suspected.
Staging is based on how extensively the cancer has spread throughout and beyond the lymphatic system, which areas are affected, and whether constitutional symptoms, such as fever, night sweats, or weight loss, are present.
The staging of MALT lymphoma is essential for precise prognosis and the development of an effective treatment plan. The Lugano classification system, a modification of the long-used Ann Arbor Staging System, is widely used for staging non-Hodgkin lymphoma. Staging for gastric MALT lymphoma includes Stages I, II, and IV. There is no Stage III.
Treatment and therapy: When bacteria are present in the tumor tissue, biological therapy, such as intensive antibiotic treatment, often leads to a complete lymphoma remission. Approximately 70 to 80 percent of patients will have complete regression of malignancy with antibiotic treatment of H. pylori when MALT lymphoma is limited to the stomach. If antibiotics do not clear MALT lymphomas or the disease spreads, other treatments are given, including radiotherapy, surgery, or chemotherapy.
Some MALT lymphomas grow very slowly, especially if the site of origin is other than the stomach and may not cause any problems for many years. In this case, treatment may not be needed immediately, and active monitoring is used instead. If patients have been treated for a lymphoma affecting the stomach, they typically undergo regular follow-up endoscopies and biopsies of the stomach to look for signs of recurrence. Bruton's tyrosine kinase (BTK) inhibitors like ibrutinib (Imbruvica) and zanubrutinib (Brukinsa) are often used in reoccurring MALT lymphoma.
The typical treatment for MALT lymphoma affecting the lung or bowel is chemotherapy. Low-grade MALT lymphoma may transform into high-grade lymphoma, which requires intensive chemotherapy. Side effects of non-Hodgkin lymphoma management may vary depending on what part of the body is affected and the treatment used. The side effects of biological therapy are most often flu-like symptoms, and external radiation to the abdomen may cause nausea, vomiting, and diarrhea.
MALT lymphoma may be removed during a surgical operation. If the lymphoma affects the stomach, a total gastrectomy may be needed. This involves removing all of the stomach and the lower part of the gullet. The gullet is then joined directly to the small intestine.
Prognosis, prevention, and outcomes: The International Prognostic Index is the most widely used prognostic system for non-Hodgkin lymphoma, and it was designed to further clarify lymphoma staging. Paradoxically, in a significant number of cases, aggressive lymphomas can be cured by chemotherapy, while indolent non-Hodgkin lymphomas generally cannot be cured. Approximately 40 percent of indolent malignancies transform into high-grade aggressive lymphomas, and the cure potential of the transformed lymphoma is less favorable than that of aggressive lymphomas without transformation.
Bibliography
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Min, Gi-June, et al. “Long-term Clinical Outcomes of Gastric Mucosa-associated Lymphoid Tissue Lymphoma in Real-world Experience.” Annals of Hematology, vol. 102, no. 4, 2023, pp. 877-888. doi:10.1007/s00277-023-05130-8.
"Non-Hodgkin Lymphoma Stages." American Cancer Society, 15 Feb. 2024, www.cancer.org/cancer/types/non-hodgkin-lymphoma/detection-diagnosis-staging/staging.html. Accessed 20 June 2024.
Wöhrer, Stefan, et al. "Retrospective Comparison of the Effectiveness of Various Treatment Modalities of Extragastric MALT Lymphoma: A Single-Center Analysis." Annals of Hematology, vol. 93, no. 8, 2014, pp. 1287–95. doi:10.1007/s00277-014-2042-z.