Splenic Marginal Zone B Cell Lymphoma

Definition

B cell neoplasm composed of small and medium sized cells that involves the mantle and marginal zones of splenic follicles and the splenic red pulp

Polymorphous population with mantle and marginal zone distribution
- Small round lymphocytes surround and replace follicles (follicular colonization)
  - Results in micronodular pattern
- Medium sized cells with clear cytoplasm in surrounding marginal zone
  - Scattered large blasts may be intermixed
- Occasional features
  - Plasmacytoid differentiation
  - Epithelioid histiocytes
Red pulp infiltrated by small nodules of mixed sized cells
- Small cells invade sinuses
Marginal zone type lymphocytes may be numerous
- Small cells with clear cytoplasm
Peripheral blood may show villous lymphocytes
- Lymphoid cells with short polar villi
- Plasmacytoid differentiation may be seen
- Not all cases or cells show villi
- 65% of cases have some kind of circulating lymphocytes
Marrow involved in 95% of cases
Splenic hilar nodes frequently involved
- May not show distinct marginal zone distribution
- More mixing of small and medium sized cells
Lacks specific markers of other small cell lymphomas
- Negative to infrequent for CD23, bcl1, CD5, CD10
- Positive for B lineage markers and bcl2
- No specific positive immunologic marker
  - Immunologically, a diagnosis of exclusion
Lacks features of nodal or extranodal marginal zone lymphomas
- No peripheral node involvement
- No extranodal tissue involvement
Transformation reported in 13% of cases
- Large B cell lymphoma

Yasodha Natkunam MD PhD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting:: May 1, 2006