The purpose of this study was to explore the histopathological staging and differential diagnosis of marginal zone lymphoma in gastric mucosa-associated lymphoid tissue (MALT lymphoma). We performed detailed histomorphology and immunohistochemistry investigations as well as genetic testing on endoscopic biopsy and endoscopic mucosal resection specimens from 18 patients with gastric MALT lymphoma. We found that gastric MALT lymphoma typically begins as a small, isolated area outside the lymphoid follicular mantle zone or proliferates in a multifocal, patchy manner, gradually spreads to the interfollicular zone, forming diffuse proliferation, invades the gastric mucosal glands, and infiltrates or proliferates into the center of peripheral reactive lymphoid follicles. Abnormally proliferating lymphocytes invade the surrounding lymphoid follicles, resulting in damage, atrophy, and disappearance of their normal follicles as well as of the gastric mucosa glands, forming diffuse proliferation. Redifferentiation and proliferation lead to the transformation of lymphocytes; that is, MALT transitions into highly invasive lymphoma. Based on our findings in this study, we propose the following five stages in the process of development and progression of gastric MALT lymphoma: the stage of cell proliferation outside the lymphoid follicular mantle zone; the stage of heterogeneous proliferative lymphoepithelial lesion; the stage of reactive lymphoid follicular implantation; the stage of lymphoid follicular clonal proliferation; and the stage of MALT transforming into highly invasive lymphoma. We examined the differential diagnosis of histopathological features at each stage. The clinicopathological staging of gastric MALT lymphoma can help clinicians provide accurate treatment and track malignant cell transformation, thus playing a significant role in controlling its development and progression.
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