A 62-year-old man is evaluated for abdominal pain. Computed tomography (CT)
shows a 7-cm mesenteric mass. An incisional biopsy reveals a diffuse large B-cell
lymphoma, and immunohistochemical staining is positive for the B-cell antigen
CD20. The patient is referred to an oncologist. A positron-emission tomographic–CT
(PET-CT) scan reveals involvement of additional nodes in the lower chest and abdomen.