Composite mantle cell lymphoma and chronic lymphocytic leukemia/small lymphocytic lymphoma

Background: Composite mantle cell lymphoma (MCL) and chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) is rare, as less than 20 cases have been reported so far. However, this entity may be under-diagnosed because the two lymphomas are very similar in morphology and immunophenotype. Previous cases were mostly diagnosed with immunohistochemistry, but flow cytometry may play an important role in the detection of two tumors in the same specimen, thus achieving an accurate diagnosis. By definition, a composite lymphoma is two demarcated lymphomas occurring at the same anatomic site. Therefore, immunohistochemistry is still needed to identify the topographic relation of these two tumors. Our reported case illustrates the pitfalls in the diagnostic process and we recommend two standard panels with new markers for an accurate diagnosis of this composite lymphoma. Method: FACSCanto II is used with antibodies, including CD5, CD10, CD19, CD20, CD22, CD23, CD43, CD79b, CD200, kappa, and lambda. Immunohistochemical stains include PAX-5/CD5 dual stain, Cyclin D1, SOX11, and LEF-1. Results: CLL/SLL is positive for CD5, CD19, CD23, CD43, and CD200, with dim expression of CD20, CD22, CD79b, and kappa. MCL is positive for CD5, CD19, CD20, CD22, CD79b, kappa, and negative for CD23, CD43, and CD200. Immunohistochemical stains show that PAX-5/CD5 stains the entire tumor population. Cyclin D1 and SOX11 only stain the central portion that represents MCL and LEF-1 stains the periphery that represents CLL/SLL. Conclusions: We recommend the use of the above panels for flow cytometry and immunohistochemistry, respectively. LEF-1 is specific for CLL/SLL; and CD200 is helpful to distinguish CLL/SLL from MCL.