Mucosa-associated lymphoid tissue (MALT) lymphoma of the stomach progressing to overt B cell malignancy.

A 70 year old man, who underwent subtotal gastrectomy under the diagnosis of reactive lymphoid hyperplasia 6 years earlier, suffered from diffuse large-cell-type B cell lymphoma in the remnant stomach. Retrospectively reviewed, the initial lesion was consistent with mucosa-associated lymphoid tissue (MALT) lymphoma, a low-grade B cell malignancy, based upon histologic, cytologic and immunohistochemical features. Both the initial and recurrent tumors revealed the phenotypes of mantle zone cells, DBA44-positive. It is noteworthy that the overt lymphoma cells retained the capacity for inducing germinal center-like nodules consisting of LN1 and DNA7-positive cells even in the invading site. The diagnosis of reactive lymphoid hyperplasia of the stomach should be made after careful exclusion of the possibility of MALT lymphoma.