SPLENIC MARGINAL ZONE LYMPHOMA - A DISTINCTIVE TYPE OF LOW-GRADE B-CELL LYMPHOMA - A CLINICOPATHOLOGICAL STUDY OF 13 CASES

The recognition and classification of the different varieties of splenic low-grade B-cell lymphomas have been hampered by the rarity of histological studies of surgical splenectomy specimens of B-cell lymphoma. In an effort to characterize the recently described splenic marginal zone lymphoma (SMZL), we conducted a survey of 13 patients with this type of tumor using the criteria defined by Schmid for its recognition (Schmid et al., Am J Surg Pathol 1992;16:455-66). Primary splenic high-grade lymphomas, T-cell lymphomas, and secondary infiltration by other recognized low-grade B-cell lymphomas, with the exception of splenic lymphoma with villous lymphocytes, were excluded. This selection gave rise to a homogeneous group of tumors with similar clinical, histological, immunohistochemical, and molecular features. Our study showed the critical parameters for their recognition to be morphological, including macroscopic micronodularity and the constant presence of white- and red-pulp infiltration, marginal zone pattern, and plasmacytic differentiation. No t(14;18) or PRAD-1/cyclin D1 overexpression was detect able in any case. Clinically, the tumors were widespread with a protracted evolution. Nodal infiltration by SMZL in our cases was morphologically similar to monocytoid B-cell lymphoma. SMZL could constitute the largest group of primary splenic malignant lymphomas, partially overlapping with splenic lymphoma with villous lymphocytes. Specific molecular markers for SMZL have yet to be defined. Because of the limited number of cases, the question of therapy for this group of lymphomas must remain open for the future.