Splenic marginal zone lymphoma (SMZL) without or with villous lymphocytes (SLVL) is a low grade B cell non-Hodgkin’s lymphoma that comprises <1% of lymphoid malignancies. SLVL is indistinguishable histologically from SMZL and it is believed that the 2 entities represent different phases of the same process in the spleen and the bone marrow. Characteristic features of SMZL are splenomegaly, moderate lymphocytosis, immunophenotype with a CLL score < 2 and nodular/intrasinusoidal pattern of bone marrow infiltration. Despite its slow clinical course, and response to splenectomy, approximately 50% of deaths in patients with SMZL are caused by progressive disease. As in other low grade lymphoproliferative disorders, SMZL may undergo high grade transformation. We describe 8 cases of SMZL that showed clinical, morphological and histological features of progression to large B cell lymphoma. These 8 cases represent 19% of our series of 41 SMZL patients followed up between 1996 and 2006. Patients were aged between 44 and 76 years, and there were 4 men and 4 women. Progression to high grade B cell lymphoma occurred between 1 and 48 months from diagnosis. The cases can be divided into 2 distinct groups on the basis of the site of transformation. Those cases with high grade transformation in the bone marrow had a median overall survival of 10 months, although 1 patient did attain a complete remission with combination chemotherapy (R-CHOP) and is alive at 12 months. In contrast, there were 3 cases of transformation in peripheral lymph nodes with a median overall survival of 60 months. Large B cell lymphoma was also diagnosed in the spleen in the initial stages of the disease in 1 case. This patient achieved a complete remission with R-CHOP post splenectomy, and is still alive at 36 months follow up. In a previous report of transformation to large B cell lymphoma in SMZL (Camacho et al, Am J Surg Pathol 2001) a 13% incidence was reported. In our series of 8 cases the incidence of transformation is 19%. Hence it appears that while the incidence of large B cell transformation seems to be higher than in CLL (1–10%) it is lower than that reported in follicular lymphoma (25–60%). Two of the 4 cases of high grade transformation in the bone marrow had previously been treated with fludarabine in the year prior to their progression to large B cell lymphoma. In 1 of these cases Epstein Barr Virus encoded RNA was detected in the malignant cells at the time of transformation. This may suggest that EBV is involved in the pathology of SMZL transformation, and treatment with immunosuppressive agents such as the purine analogues, may increase this risk. In our series of 41 patients, 6 have received fludarabine therapy and the risk of high grade transformation in this small group is significantly higher at 33% (2/6).

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