A 54-year-old man is evaluated for a 3-month history of worsening dyspepsia, gastric bloating, and abdominal discomfort. His dyspepsia has so far been treated with ranitidine. The patient is allergic to penicillin.
On physical examination, the patient is afebrile, blood pressure is 112/70 mm Hg, pulse rate is 83/min, and respiration rate is 14/min. BMI is 25. No palpable lymphadenopathy is present. Abdominal examination reveals mild epigastric tenderness. The remainder of the examination is unremarkable.
The hemoglobin level is 11.5 g/dL (115 g/L). Complete blood count and differential are otherwise normal. Results of fecal occult blood testing are positive.
Upper endoscopy shows several small gastric ulcers. Histopathologic studies reveal evidence of Helicobacter pylori infection and small clonal mucosa-associated B cells expressing the CD20 antigen consistent with mucosa-associated lymphoid tissue lymphoma. A CT scan of the abdomen shows no evidence of lymphadenopathy.
Ranitidine is discontinued.
Which of the following is the most appropriate management?