The stomach is the most common site of extranodal lymphoma.
Epidemiology
Extranodal marginal zone lymphoma makes up about 5% of gastric malignancy. A smaller number of lymphomas are diffuse large B cell lymphoma; an even smaller number arise in patients who take oral immunosuppressive agents.
Aetiology and Pathogenesis
Extranodal marginal zone lymphomas arise in areas of chronic inflammation. In the stomach, they are strongly associated with Helicobacter pylori infection. This creates a lymphomatous inflammatory infiltrate within the stomach which has the potential to become malignant. A significant number of diffuse large B cells arise from extranodal marginal zone lymphoma. EBV related extranodal lymphomas can arise in conjuction with oral immunosuppressive therapy.
Natural History
These lesions are typically indolent but can spread diffusely throughout the stomach. Distant metastases are rare except in cases of transformation to DLBCL.
Clinical Presentation
Presentation is similar to gastric ulceration or gastric carcinoma. Patients complain of dyspepsia and upper abdominal pain. B symptoms are uncommon. Patients may be anaemic, or complain of haematemesis or melaena.
Tumour Features
Extranodal Marginal Zone Lymphoma
Extranodal marginal zone lymphoma diffusely infiltrates the stomach, causing thickening of the gastric folds and nodularity. On microscopy, there is a monomorphic infiltration of small malignant lymphocytes. They are arranged in lymphoepithelial lesions within the gastric muscosa and submucosa.
Immunohistochemistry is positive for CD19, CD20 and CD43 (the latter is fairly specific). There are several translocations seen in extranodal marginal zone lymphoma, and interestingly the most common does not involve chromosome 14. Instead, translocation of chromosomes 11 and 18 occurs; forming a hybrid protein product. Translocation of chromosome 14 with chromosome 18 can also occur.
DLBCL
This tumour contains large, malignant lymphocytes which diffusely infiltrate the normal tissues. They are similar to DLBCL in other sites.
