Characteristics of CD5-Positive Splenic Marginal Zone Lymphoma with Leukemic Manifestation; Clinical, Flow Cytometry, and Histopathological Findings of 11 Cases

Splenic marginal zone lymphoma (SP-MZL) is a rare low-grade B-cell neoplasm that often shows leukemic manifestation. Less than 20% of cases of SP-MZL express CD5. We analyzed 11 cases of CD5-positive SP-MZL with leukemic manifestation. The clinical characteristics of these cases did not differ from those of CD5-negative SP-MZL. Flow cytometry revealed positive results as follows : CD3, 0/9; CD5, 11/11; CD10, 0/11; CD11c, 4/10, CD13, 5/11; CD19, 11/11; CD20, 10/11; CD21, 4/4; CD22, 7/7; CD23, 5/10; CD25, 8/11; FMC7, 5/7; k type 6/9, and lambda type 2/9. All 3 cases with monoclonal gamma-globulinemia expressed CD13. Resected spleen exhibited a proliferation of neoplastic cells in white pulp in all 8 splenectomy patients and a marginal pattern was detected in 5 patients. Only 2 cases showed involvement of red pulp. Immunohistochemistry showed that the lymphoma cells were positive for CD5, CD20, and BCL-2 and negative for CD3, CD10, cyclin D1, BCL-6, and MUM-1 in all 11 cases. These results suggest that CD5-positive SP-MZL differs from B-cell chronic lymphocytic leukemia, that CD13 expression is found in about half of CD5-positive SP-MZL cases, and that CD5-positive SP-MZL may be related to memory B-cell neoplasm or plasma cell differentiation.