CD5+ follicle center lymphoma. Immunophenotyping detects a unique subset of "floral" follicular lymphoma.

The "floral" variant of follicle center lymphoma (FCL) may be confused with progressive transformation of germinal centers or lymphocyte predominance Hodgkin lymphoma. Immunohistochemistry and gene rearrangement studies are usually sufficient to differentiate among these entities. We present 11 cases of floral FCL that were evaluated at our institution by flow cytometry, immunohistochemistry, or both and by polymerase chain reaction-based molecular analysis. In 4 cases, the neoplastic B cells coexpressed CD5 antigens; 3 of these 4 cases also were CD10+, and all demonstrated rearrangement within the bcl-2 locus. These findings demonstrate that a subset of floral FCL is CD5+. Recognition of this immunophenotype is important to avoid misdiagnosis of nodular variants of small lymphocytic lymphoma and mantle cell lymphoma. Studies suggest that expression of CD5 by neoplastic germinal center cells might result from alterations of the follicular microenvironment and/or inappropriate B-cell responses to cytokine networks.