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The report by Millar and colleagues1 of aberrant expression of CD10, the common acute lymphoblastic leukaemia (ALL) antigen, by the cells of a marginal zone non-Hodgkin's lymphoma (NHL) is important because it reminds histopathologists not to rely too heavily on the results of single surface marker tests. “Aberrant” expression of CD antigens by malignant lymphohaemopoietic cells is a phenomenon with which haematologists have long been familiar; expression of “myeloid” antigens CD13 and CD33 by the blast cells of common ALL and the “B lymphoid” antigen CD19 by those of acute myeloid leukaemia with the t(8;21) translocation are two classic examples. But is not the range of CD10 positive NHL cases already rather broader than they suggest? We have known for years that up to 20% or so of lymphoblastic lymphomas have an immunophenotype indistinguishable from common ALL and that a similar proportion of T cell lymphoblastic lymphomas, albeit not acknowledged by the REAL classification,2 may also express CD10. In addition, the REAL classification also points out that some cases of mantle cell and diffuse large B cell lymphoma express CD10.
The range of monoclonal antibodies that work superbly on sections of formalin fixed, paraffin wax embedded tissue is steadily expanding. The wider use of comprehensive panels of antibodies in the diagnosis of NHL, whether on sections or by flow cytometry or both, will surely reveal more “aberrant” results, and may even modify our views about what “aberrant” means.