Diffuse large B-cell lymphoma (DLBCL) in a gastric biopsy from an elderly male who presented with gastritis. The lymphoma cells diffusely infiltrate in between the gastric glands causing wide separation and disrupting the native architecture. They have round, oval, or irregular nuclei, multiple punctate nucleoli, and scant cytoplasm. The morphologic and immunophenotypic findings (see slides 38-44) were diagnostic of DLBCL. In some cases, the tumor cells may infiltrate into the overlying epithelium causing mucosal ulceration. About one third of cases have a concomitant component of low-grade marginal zone lymphoma (i.e. they have arisen by large cell transformation of a MALToma).