Rosette formation in malignant lymphoma.

Lymph node biopsies in a patient with follicular lymphoma showed rosette structures as seen in neuroepithelial neoplasms. These specimens were studied by histologic, immunoperoxidase (for immunoglobulins, intermediate filaments (IF), actin and neuron-specific enolase), immunofluorescence (for immunoglobulins, and with a panel of monoclonal antibodies), and electron-microscopic examination. The rosettes were formed by neoplastic lymphocytes arranged around eosinophilic fibrillary material. Ultrastructurally, this was composed of cytoplasmic processes, projecting from the lymphocytes and containing thin and intermediate filaments. Immunohistochemically, it stained for monoclonal IgM lambda, all other antigens present on the neoplastic cells, and weakly for vimentin and actin. Based on recent information about lymphocyte surface changes, it is speculated that the rosettes might represent an aggregation of neoplastic lymphocytes activated by a microenvironmental stimulus, perhaps antigen-antibody binding at the cell membrane. The practical implication of this hitherto unreported finding is that the presence of rosettes cannot be used to rule out a lymphoma.