Splenic Marginal Zone Lymphoma

General: Splenic marginal zone lymphoma (SMZL) is an uncommon lymphoma and probably accounts for less than 3% of lymphomas. The median age at diagnosis is 68 years with a slight male predominance.39 It presents with splenomegaly and peripheral blood involvement is common. The appearance in the peripheral blood accounts for the term splenic lymphoma with villous lymphocytes. Adenopathy is uncommon and a small monoclonal gammopathy is present in up to two-thirds of patients.40

Pathology: Peripheral blood morphology is variable. The cells are small with moderate amounts of pale cytoplasm and short cytoplasmic projections that may aggregate at opposite ends of the cells. Nucleoli are inconspicuous. At times the cells lack noticeable projections and have a more monocytoid or plasmacytic appearance.

In the spleen, there is expansion of the white pulp. Marginal zones may be expanded and a nodular appearance can be seen from replacement of the preexisting follicles. The cells have a variable appearance with small lymphocytes having scant cytoplasm often seen at the centers of the nodules and monocytoid B-cells with more abundant cytoplasm present at the edges of the nodules (Figures 52.8 and 52.9). Transformed centroblastic cells are present and there may be plasmacytic differentiation. There is always extension into red pulp that can be highlighted by immunohistochemistry. Hilar lymph nodes are usually

Figure 52.8 Splenic marginal zone lymphoma. Low magnification shows expansion of the white pulp with prominent marginal zones. The inset (upper left) shows a circulating lymphoma cells with villous cytoplasmic projections
Figure 52.9 Splenic marginal zone lymphoma. High magnification shows the characteristic cytologic features of small cells with abundant pale cytoplasm. The upper right corner shows part of a germinal center surrounded by a thin rim of mantle cells

involved with replacement of the germinal centers but patent sinuses.4142 Bone marrow involvement is often in a sinusoidal distribution but the pattern is not entirely specific.43'44

Immunophenotype: The immunophenotype is CD5-, CD10-, CD19+, CD20+, CD22+, CD25-/+, CD103-, bcl-2+, bcl-6-, surface Ig+.17,45,46

Molecular genetics: Recent studies have show frequent deletion of 7q31-32 in SMZL.47 Other common abnormalities include gain of 3q and abnormalities of chromosomes 1, 8, and 14.48 Note that translocations of MLT1 seen in extranodal marginal zone lymphomas of MALT type are not seen in SMZL, thus further supporting the contention that these are unrelated disor-ders.49 Cases with chromosomal losses, including del 7q, may identify cases with a poor survival.50 IGH mutational analysis shows, as in CLL, heterogeneity within SMZL and cases. Unmutated SMZL appeared to have a shorter overall survival and del 7q31 was over-represented in this group.50

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