MONOCYTOID B-CELLS - A COMPARATIVE CLINICAL-PATHOLOGICAL STUDY OF THEIR DISTRIBUTION IN DIFFERENT TYPES OF LOW-GRADE LYMPHOMAS

Neoplastic monocytoid B-cells (MBCs) are present in different amounts in several types of non-Hodgkin's lymphomas (NHLs), including monocyto id B-cell lymphoma (MBCL), splenic marginal zone lymphoma (SMZL), muco sa-asssociated lymphoid tissue (MALT) low-grade B-cell lymphomas, and follicular centroblastic-centrocytic (CB-CC) lymphomas. In an attempt to clarify the relationships between different groups of tumors with a significant monocytoid component, we studied six primary lymph node M BCL, three SMZL, seven MALT lymphomas, and four CB-CC with monocytoid differentiation. Their clinical, morphological, immunohistochemical an d molecular features were compared. The results show wide overlapping between MALT and MBCL in terms of morphology, immunophenotype, and mol ecular features. Follicular colonization was a characteristic finding in both groups. Some MBCL revealed mucosal involvement during the cour se of the disease, suggesting a possible MALT origin. Our data support the suggestion that the use of the term MBCL should be discontinued i n cases with mucosal involvement, as they are probably examples of lym ph node involvement brought about by MALT lymphomas. Although SMZL hav e some overlapping features with MBCL and MALT lymphomas, some of the clinical and morphological specific findings justify their distinction from the other groups. The CB-CCs with monocytoid differentiation fre quently harbored t(14;18), lacking any significant differentiating fea tures from conventional follicular CB-CC lymphomas. Additional studies are needed to define the molecular features of MBCL and other margina l zone tumors.