A 65-year-old woman presents to the physician's office with a 6-month history of epigastric discomfort, poor appetite, and 10-lb weight loss. Past history is pertinent for hypertension, diabetes, a 30 pack-year smoking history, and occasional alcohol intake. Examination is unremarkable except for mild epigastric tenderness to deep palpation. An abdominal ultrasound reveals cholelithiasis, and one view of a UGI x-ray series is shown in the figure.

Which of the following is the most likely diagnosis?