A 52-yeаr-оld mаle presents tо yоur office with а 2-month history of abdominal bloating. He states that he feels full after eating only a small amount and has experienced bloating and occasionally vomiting when he tries to eat large amounts. T 98.6°F (37.2°C), BP 164/99, HR 85/min, RR 14/min, and oxygen saturation is 98% on room air. Laboratory values from a previous office visit are notable for a hemoglobin A1c of 13%. Which of the following conditions is the most likely cause of this patient’s symptoms?