one of the most common types of aggressive lymphoma, comprising about 20% of all cases of non-Hodgkin lymphoma; the patients' median age is 57 years. The cell of origin is the B lymphocyte despite its prior classification as one of the histiocytic lymphomas. About 20% of the cases have good evidence for a follicular center cell origin due to the presence of the BCL-2 gene rearrangement. As aggressive malignancies with a tendency to metastasize, most eventually demonstrate some extranodal component, including the gastrointestinal tract, testes, skin, central nervous system, or bone.