Utility and diagnostic pitfalls of SOX11 monoclonal antibodies in mantle cell lymphoma and other lymphoproliferative disorders.

Mantle cell lymphoma (MCL) is classically characterized by t(11;14) leading to cyclin D1 overexpression. Recently the transcription factor SOX11 has been discovered to be expressed in most MCL, including cyclin D1-negative cases. In this study we assess the performance of 2 commercially available monoclonal antibodies, Atlas Antibodies (Stockholm, Sweden) clone CLO142 and Cell Marque (Rocklin, CA) clone MRQ-58, for SOX11 immunohistochemistry in MCL, both cyclin D1 positive and cyclin D1 negative, as well as in cases of other small B-cell lymphoproliferative disorders, diffuse large B-cell lymphomas (DLBCLs), Burkitt lymphomas, and lymphoblastic leukemia/lymphomas. We also performed Western blots to further characterize the antibody specificity. Both antibodies show reliable, clear nuclear staining in MCL with variable specificity. However, the MRQ-58 antibody was more specific for MCL than CLO142, which showed considerably more nonspecific staining, especially in DLBCLs (59% positive vs. 4% positive with MRQ-58). In addition we reconfirmed the utility of SOX11 IHC for identifying cases of cyclin D1-negative blastoid MCL. However, we also identified cases of SOX11-positive DLBCL and splenic marginal zone lymphoma. Although SOX11 IHC is a powerful, and relatively accessible, tool to identify MCLs with variant immunophenotypes and/or morphology, these latter 2 cases highlight the need for strict criteria for interpreting SOX11 staining.