The distinctive low-grade B-cell mucosa-associated lymphoid tissue lymphoma (MALToma) of the extranodal lymphoid tissue has been well characterized in recent years. One hundred cases of gastrectomized primary gastric lymphomas, 30 cases of surgically resected primary intestinal lymphomas and five cases of autopsied pulmonary lymphomas were examined clinicopathologically. Fortyone cases of gastric lymphomas, nine cases of intestinal lymphomas and four cases of pulmonary lymphomas were classified as MALToma by using Isaacson's classification. Morphological feature of MALToma was lymphoepithelial lesion. All of gastric MALTomas were found out in advanced stage. Pulmonary lymphoma cases were not diagnosed correctly during life. Metastasis in gastrointestinal tract and serous membrane were seen in four cases of pulmonary MALToma. Tumor cells of MALTomas share an identical phenotype with splenic marginal zone B-cells. We examined the experimental gastric ulcer of rat by using immunohistochemistry. Centrocyte-like cells foci were observed in the ulcer bed, which express the phenotypical characters as same as splenic marginal zone B-cells. We discussed the cytopathological features of MALToma from the viewpoint of B-cell lineages.
