Primary gastrointestinal lymphomas: a classification of 66 cases.

Using routine histology, resin embedded sections and immunohistochemical techniques on formalin-fixed, paraffin processed tissue, 66 cases of primary gastrointestinal lymphoma have been classified. This study necessitated the development of reliable criteria to separate lymphomas of true histiocytic origin from those of lymphocytic origin. Among the morphologic properties of malignant histiocytes were complex pleomorphic nuclei, abundant well delineated cytoplasm and phagocytosis. These cells were shown to contain all major immunoglobulin chains, C3, lysozyme and in some cases alpha 1 antitrypsin. Malignant lymphomas derived from histiocytes could be divided into two groups: malignant histiocytosis of the intestine (MHI), a recently described diffuse pleomorphic lymphoma associated with villous atrophy of the small intestine, and histiocytic lymphoma (HL) which forms solid tumor masses in a similar manner to lymphocyte derived tumors. Immunohistochemical studies of lymphocyte derived tumors were negative apart from one case with plasmacytoid differentiation. Of the 66 cases, 50% were of histiocytic origin (33% MHI, 17% HL) and 41% of lymphocyte origin, there was one case of Hodgkin's disease and five cases were unclassified. The role of the histiocyte in gastrointestinal mucosa deserves further study.