A novel CD11c monoclonal antibody effective in formalin-fixed tissue for the diagnosis of hairy cell leukemia

Objective: The diagnosis of hairy cell leukemia (HCL) and its distinction from other B-cell lymphomas can be difficult in formalin-fixed tissue. This is because the histology is not always classical, and despite having a characteristic phenotype, there are few relevant monoclonal antibodies with sufficient sensitivity and specificity that can be applied to fixed material. In this study, we assessed the utility of a newly developed antibody against a formalin-resistant CD11c epitope (5D11) for the diagnosis and monitoring of HCL in formalin-fixed tissue. Methods: We performed immunohistochemical staining for CD11c expression in formalin-fixed and also decalcified tissue of 196 small B-cell lymphomas, including 104 cases of HCL showing extensive to minimal infiltrates. Results: The CD11c antibody was both sensitive and specific for HCL, even in cases with minimal infiltration. Conclusion: We recommend that this CD11c antibody be added to a panel of antibodies for immunostaining of formalin-fixed material, for differentiation of HCL from other small B-cell lymphomas, and for detection of residual disease following therapy. Copyright (c) 2008 S. Karger AG, Basel.