MALT lymphomas are extranodal lymphomas that appear to arise from B lymphocytes located in the marginal zone of lymphoid follicles. Although there is a substantial amount of lymphoid tissue in the gastrointestinal tract, MALT lymphomas usually arise in chronically inflamed sites that are normally devoid of lymphoid tissue. The best example is gastric MALT lymphoma that is almost always associated with Helicobacter pylori. Another example is immunoproliferative small intestinal disease (alpha heavy-chain disease) although the inflammatory stimulus continues to be unclear. Primary MALT lymphomas have also been described outside of mucosal surfaces but usually in the presence of chronic inflammation. One example is hepatic MALT lymphomas that have been associated with disorders such as hepatitis C and primary biliary cirrhosis. Most MALT lymphomas have an indolent course with an overall 5-year survival of 80% or more. A minority transform to a diffuse large B-cell lymphoma with a poorer prognosis. Management options are influenced by the site, size and spread of lymphoma but include simple observation, antibiotics (H. pylori, immunoproliferative small intestinal disease), radiotherapy and chemotherapy. The patient illustrated below was diagnosed with MALT lymphoma of the pancreas 12 years after surgery for gastric MALT lymphoma.
A 62-year-old man was referred for evaluation because of the finding of a swollen pancreas on a computed tomography (CT) scan. Twelve years previously, he had a total gastrectomy for a gastric MALT lymphoma. Serum levels of carbohydrate antigen 19.9, carcinoembryonic antigen and IgG4 were within the reference range. A contrast enhanced CT scan showed that the tail of the pancreas was enlarged with patchy low-density lesions (Figure 1 above). A positron emission tomography/CT scan showed strong diffuse uptake of fluorodeoxyglucose throughout the pancreas (Figure 1, below). Endoscopic ultrasound with fine-needle aspiration revealed atypical small lymphoid cells with condensed chromatin as well as larger lymphoid cells (Figure 2, above). Immunohistochemical stains were positive for CD20 (Figure 2, below) and BCL-2 and negative for CD10, CD3 and CD5. This immunophenotype reflects that of marginal zone B cells and is typical of a MALT lymphoma. In this case, the development of a pancreatic MALT lymphoma seems more likely to be related to spread from the gastric lymphoma than the development of a second primary lymphoma.