A 35-year-old man has had epigastric pain for more than I year. The pain tends to occur 2 to 3 hours after a meal and is relieved if he takes antacids or eats more food. He has noticed a 4-kg weight gain in the past year. He does not smoke and drinks 1 glass of Johannisberg Riesling daily. The result ot a urea breath test is positive, and a gastric biopsy specimen con- tains urease. He begins a 2-week course of antibiotics, but on day 4, he feels better and discontinues treatment. Three weeks later, the epigastric pain recurs. If he does not seek further t,which of the following complications is he most likely to develop?