Expression of bcl-6 and CD10 in primary mediastinal large B-cell lymphoma - Evidence for derivation from germinal center B cells?

Primary mediastinal large B-cell lymphomas (LBCLs) constitute a unique subt ype of diffuse LBCLs, with distinct clinical, immunophenotypic, and morphol ogic features. These lymphomas are thought to originate from the thymus, an d it has been hypothesized that they derive from a population of B lymphocy tes normally present in the thymic medulla. Most diffuse LBCLs harbor somat ic mutations in their immunoglobulin genes, suggesting that they have been exposed to the germinal center. To investigate the possible relationship of mediastinal LBCLs to germinal center B cells, we analyzed the expression o f bcl-6 and CD10 in 19 mediastinal LBCLs, using an immunoperoxidase techniq ue on formalin-fixed tissue. We found that 19 of 19 (100%) mediastinal LBCL s were bcl-6+ and 6 of 19 (32%) mediastinal LBCLs were CD10+. Because media stinal LBCLs usually lack BCL-6 gene rearrangement or mutations, expression of bcl-6 and CD10 in these tumors tends to support a germinal center deriv ation.