[Normal lymphoid tissue and primary malignant lymphomas of the gastrointestinal tract]

Malignant lymphomas (ML) are malignant proliferations of lymph cells which have become blocked at a certain stage in their feto-embryonic development and, above all, that of their immune response. In order to understand the various forms of primary LM of the gastrointestinal tract, it is necessary to be aware of the various types of B and T cells present in the mucosae associated lymphoid tissue (MALT). After a morphologic and immunophenotypic description of the constituting elements of MALT, the different types of gastrointestinal M and T ML are reviewed. The features which distinguish them from ML of the lymph nodes and spleen are indicated. Three main types should be highlighted. Firstly, the centrocytic ML and/or MALT-type lymphoplasmocytic ML, which has low malignancy and are the most common. The cases previously described as "pseudo-lymphomas" are in fact true ML belonging to this group. Secondly, the B ML, which are highly malignant may or may not be preceded by or associated with a low-malignancy ML of the MALT-type. Thirdly, T ML, which are always unusual and highly malignant and which correspond to the malignant proliferation of intra-epithelial T lymphocytes. A malabsorption syndrome may precede or accompany this form, which may in other cases be accompanied by marked eosinophilia. The place of MALT-type ML in the Kiel classification is discussed.