Gastric low-grade
B cell lymphomas originating in mucosa-associated lymphoid tissues are composed of reactive hyperplastic germinal centers and interfollicular centrocyte-like cells. Their polymorphic, histologic composition and infrequent dissemination beyond the gastric wall led to the denomination of these
tumors as "
pseudolymphomas." To elucidate their clonal character, a Southern blot study of
DNA and immunohistological study was carried out on 14 cases of surgical specimens from
gastrectomy (11 low-grade and three high-grade
tumors). Monoclonal and polyclonal
antibodies were used on frozen and
paraffin sections. A mucosa-associated lymphoid tissue origin for the
tumors was assigned due to their centrocyte-like morphology and the presence of lymphoepithelial lesions. Southern blot analysis of
DNA and immunohistological results confirm the monoclonal composition of gastric
low-grade lymphomas in all cases. Although both types of technique correlated well on the predominant light-chain, Southern blot
DNA study was nevertheless more sensitive than the immunohistochemical techniques. Surprisingly, in two cases of gastric
low-grade lymphoma, Southern blot
DNA analysis of histologically reactive regional lymph nodes showed an unexpected
immunoglobulin heavy chain gene rearrangement. This coincided with that found in the gastric wall. Results confirm the monoclonal nature of the low-grade
gastric lymphoma. This supports consideration of this
tumor as an indolent primary
lymphoma of the stomach, confirming the suitability of excluding the term "
pseudolymphoma." Involvement of regional lymph nodes may be a more frequent occurrence than previously detected through morphological study.