Splenic marginal zone lymphoma

Splenic marginal zone lymphoma (SMZL) is a type of cancer (specifically a lymphoma) made up of B-cells that replace the normal architecture of the white pulp of the spleen. The neoplastic cells are both small lymphocytes and larger, transformed lymphoblasts, and they invade the mantle zone of splenic follicles and erode the marginal zone, ultimately invading the red pulp of the spleen. Frequently, the bone marrow and splenic hilar lymph nodes are involved along with the peripheral blood. The neoplastic cells circulating in the peripheral blood are termed villous lymphocytes due to their characteristic appearance. The cell of origin is postulated to be a post-germinal center B-cell with an unknown degree of differentiation. SMZL is a form of cancer known to be associated with Hepatitis C virus infection. The relevant markers that define the immunophenotype for SMZL are shown in the adjacent table. The lack of CD5 expression is helpful in the discrimination between SMZL and chronic lymphocytic leukemia/small lymphocytic lymphoma, and the lack of CD10 expression argues against follicular lymphoma. Mantle cell lymphoma is excluded due to the lack of CD5 and cyclin-D1 expression. Clonal rearrangements of the immunoglobulin genes (heavy and light chains) are frequently seen. The deletion 7q21-32 is seen in 40% of SMZL patients, and translocations of the CDK6 gene located at 7q21 have also been reported. Enlargement of the spleen is a requirement for the diagnosis of SMZL and is seen in nearly all people affected by SMZL (often without lymphadenopathy). Aside from the uniform involvement of the spleen, the bone marrow is frequently positive in patients with SMZL displaying a nodular pattern with morphology similar to what is observed in the splenic hilar lymph nodes. While nodal and extranodal involvement are rare, hilar lymph nodes adjacent to the spleen, if involved, show an effaced architecture without preservation of the marginal zone seen in the spleen.