A 59-year-old woman presents to her primary care physician with concerns about fever, night sweats, general weakness, increased fatigue, and a 15-lb unintentional weight loss over the past 3 months. Additionally, she reports mild nausea and heartburn as well as episodes of black, tarry stool in the past 10 days. She says she does not have any abdominal pain or vomiting.

The patient has mild hypertension that is well controlled with a beta-blocker. She has a history of peptic ulcer disease for which she takes omeprazole.

Physical exam reveals generalized lymphadenopathy with enlarged submaxillary, axillary, dorsal cervical, and inguinal lymph nodes that are dense and rubbery in consistency but are painless. The skin around them appears normal. Additionally, her abdomen is somewhat distended; palpation reveals hepatosplenomegaly.

Laboratory tests are ordered. A complete blood count notes presence of lymphocytosis; serum chemistry reveals elevated lactate dehydrogenase levels; and liver function tests show slightly abnormal findings.