Proliferation of marginal zone cells mimicking malignant lymphoma.

An enlarged axillary lymph node from a 58-year-old woman showed a proliferation of marginal zone cells in nodules or large band-forming aggregates within the cortex. The marginal zone cells also infiltrated the adjacent fatty tissue. They showed polytypic surface immunoglobulins (IgM++, IgG+, kappa+, lambda+). Their immunophenotype (IgD-, CD23-, KiB3-) differed from that of the small lymphocytes of the mantle zone. They were also positive for alkaline phosphatase. The lesion is reactive and must be differentiated from low-grade malignant lymphomas, especially centrocytic lymphoma.