Review Question - QID 214563

A 75-year-old man presents to the emergency department with abdominal pain that has been gradually worsening over the past month. He has severe pain whenever he eats and usually has diarrhea right after eating. As a result, he has been eating less secondary to the pain and has lost 10 pounds this month. The patient has a past medical history of diabetes, hypertension, and a 30 pack-year smoking history. His temperature is 97.5°F (36.4°C), blood pressure is 142/92 mmHg, pulse is 88/min, respirations are 12/min, and oxygen saturation is 99% on room air. The patient is currently pain free. Physical exam reveals a non-tender abdomen, clear breath sounds, and normal heart sounds. He is given a sandwich and juice which causes him to experience abdominal pain and 1 episode of diarrhea. Which of the following is the most likely diagnosis?