MALT lymphoma of the stomach is a slow-growing cancer and a type of non-Hodgkin lymphoma. It starts in the stomach and develops from immune cells called B cells. Its full name is extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue, and MALT is short for mucosa-associated lymphoid tissue. Your report may use either name, and some reports call it gastric MALT lymphoma.
The stomach is the most common site for MALT lymphoma to develop. In many people, the lymphoma is linked to a long-lasting stomach infection with a bacterium called Helicobacter pylori (H. pylori). When this infection is treated with antibiotics, the lymphoma often shrinks and disappears. This article explains what MALT lymphoma of the stomach is, how it is diagnosed, and what the findings in your pathology report mean.
MALT lymphoma can also start in other parts of the body, such as the eye area, lung, salivary gland, or thyroid. For lymphoma in those places, see our article on extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue.
Most cases of MALT lymphoma of the stomach start with a long-lasting H. pylori infection. The healthy stomach lining normally contains very few immune cells. When H. pylori infects the stomach, the body sends large numbers of immune cells, including B cells, into the lining to fight the bacteria. This causes Helicobacter gastritis, a type of long-lasting inflammation.
Over many years, the constant stimulation from the bacteria can cause one B cell to develop genetic changes and grow out of control. In the early stages, these lymphoma cells still depend on bacteria-triggered signals to keep growing. This is why removing the infection with antibiotics can make the lymphoma go away. About two out of three cases are linked to H. pylori. In the remaining cases, the lymphoma cells have developed genetic changes that allow them to grow without the bacteria.
The symptoms of MALT lymphoma of the stomach are often mild and similar to those of gastritis or a stomach ulcer. Some people have no symptoms, and the lymphoma is found during an endoscopy done for another reason.
MALT lymphoma of the stomach is usually diagnosed after an upper endoscopy. During this procedure, a doctor passes a thin, flexible tube with a camera through the mouth to look at the inside of the stomach. The lymphoma may look like gastritis, an erosion, an ulcer, thickened folds, or a small mass. Because the lymphoma can be patchy, the doctor usually takes many biopsies from both abnormal and normal-looking areas.
A pathologist then examines the tissue under a microscope. The diagnosis usually needs additional tests, including immunohistochemistry and sometimes molecular testing. These tests help distinguish MALT lymphoma from the large numbers of normal immune cells present in gastritis.
Under the microscope, MALT lymphoma of the stomach is made up of sheets of small to medium-sized B cells. These cells fill the lamina propria, the tissue that supports the glands in the stomach lining, and push the normal glands apart. Some lymphoma cells have pale cytoplasm, and others resemble plasma cells. Normal-looking immune cell clusters with germinal centers are often scattered among the lymphoma cells.
A key feature that pathologists look for is the lymphoepithelial lesion, which forms when lymphoma cells invade and damage the glands of the stomach lining. These lesions are an important clue because they are much more common in lymphoma than in gastritis.
In some cases, the lymphoma grows deeper into the stomach wall, reaching the submucosa or the muscularis propria. A small biopsy usually shows only the lining, so clinicians often measure the lymphoma’s depth with an endoscopic ultrasound rather than from the pathology report.
Immunohistochemistry is a test that uses antibodies to show which proteins are present in cells. For MALT lymphoma of the stomach, it confirms that the abnormal cells are B cells and helps rule out other types of lymphoma. Your report may describe the following results.
Pathologists look for H. pylori in every biopsy showing MALT lymphoma of the stomach because the result guides first-line treatment. The bacteria can sometimes be seen on routine slides, but many pathologists also use a special stain or an immunohistochemistry test to make the bacteria easier to find. If no bacteria are seen in the biopsy, your doctor may order a breath test, stool test, or blood test to check for the infection in another way.
Molecular tests look for genetic changes inside the lymphoma cells. Two tests are commonly used for MALT lymphoma of the stomach.
MALT lymphoma of the stomach is made up mostly of small cells, but a few scattered large B cells are normal for this disease. If the large cells form solid sheets, the pathologist will diagnose diffuse large B-cell lymphoma, a faster-growing lymphoma that needs different treatment. It can develop from MALT lymphoma, and it can also be found at the same time in a different part of the stomach. Earlier studies found this change in about 2% to 5% of people with MALT lymphoma of the stomach.
Staging describes how far the lymphoma has spread. For lymphoma that starts in the stomach or bowel, doctors usually use the Lugano staging system. Staging is based on endoscopic ultrasound, CT or PET scans, and sometimes a bone marrow biopsy, rather than on the pathology report alone.
Treatment for MALT lymphoma of the stomach depends on the lymphoma stage and whether H. pylori is present. The 2020 European Society for Medical Oncology (ESMO) guidelines recommend treating H. pylori as the first step for all people with MALT lymphoma of the stomach, regardless of stage.
After treatment for MALT lymphoma of the stomach, you will have repeat endoscopies with biopsies to check how the lymphoma is responding. These are usually done 2 to 3 months after treatment, then at least twice a year for 2 years. Response to antibiotics can be slow, and complete remission may take a year or longer.
Many pathologists describe the findings on follow-up biopsies using the GELA grading system. GELA stands for Groupe d’Etude des Lymphomes de l’Adulte, the French lymphoma research group that developed it. Your report may use one of the following four categories.
The outlook for a person with MALT lymphoma of the stomach is very good. Most people are diagnosed early, and the lymphoma usually responds well to antibiotics, radiation, or both. Most people remain well for many years after treatment. The lymphoma can return years later, which is why regular endoscopy is important even after complete remission.
The long-lasting gastritis caused by H. pylori also slightly increases the risk of developing stomach adenocarcinoma later in life. Follow-up endoscopies help your doctors monitor this risk as well.