Gastrointestinal Lymphoma and Mucosa-Associated Lymphoid Tissue

Mucosa-Associated Lymphoid Tissue Tumor

The stomach is the most common site of lymphoma in Western societies. The MALT type arises from malignant transformation of B cells that exist normally in the gut but that proliferate in the inflammatory process. Gastric tissue acquires MALT in the pathologic response to Helicobacter pylori infection. The MALT type represents 40% of gastric lymphomas.

Because MALT tumor is related to H. pylori infection, the incidence is higher where there is a greater incidence of chronic infection. Evidence has established that H. pylori has a key role in the development of MALT lymphoma. It is believed that the disease starts with H. pylori infection, which causes gastritis and initiates the immune response of T and B cells. In this tissue, MALT is formed. H. pylori –reactive T cells drive B-cell proliferation, which eventually leads to genetic abnormalities that result in aggressive tumor activity.

Tumors are often located in the antrum, but they can be multifocal in as many as 33% of patients. MALT lymphomas may appear as erosions, erythema, or ulcers. Histologically, there is invasion and partial destruction of gastric glands by tumor cells. Cells are usually small and infiltrate the lamina propria. Often, it is difficult to make the diagnosis of lymphoma when the lesions are small. However, invasion and distortion of the tissue clarify the diagnosis. MALT lymphomas are usually staged as follows:

• Stage I: tumors are confined to the mucosa.

• Stage II: tumors extend into the abdomen.

• Stage III (II _E ): tumors penetrate the serosa to involve adjacent organs.

• Stage IV: tumors are disseminated to nodal tissue and beyond, or they are supradiaphragmatic.