Design: Prospective cohort study.

Setting: University internal medicine clinics, a referral oncology center in southern Switzerland, and a gastroenterology referral center in northern Italy.

Patients: 26 patients with localized primary low-grade gastric MALT lymphoma.

Intervention: Treatment for H. pylori infection (bismuth or omeprazole or both, amoxicillin, and metronidazole for 14 days).

Main Outcome Measures: Endoscopic biopsy specimens of the gastric mucosa were obtained every 3 to 6 months after treatment for H. pylori infection.

Results: Helicobacter pylori was completely eradicated in 25 of 26 patients, but 4 patients needed second-line antibiotic treatment to eradicate the microorganism. Disappearance or almost total regression of the lymphomatous tissue was observed in 15 of the 25 evaluable patients (60%; CI, 39% to 79%); however, disappearance or almost total regression was evident in the first biopsy specimen after treatment for H. pylori infection in only 8 of the 15 patients.

Conclusions: Our study confirms recent anecdotal reports of regression of gastric MALT lymphoma after eradication of H. pylori and indicates that the growth of these extranodal lymphomas may depend on H. pylori.