<s>[INST] A 75-year-old woman comes to the office with a 2-year history of progressive dysphagia. She complains of gradually increasing difficulty in swallowing fluids and solid food. She has lost 15 pounds over the past 6 months.
Physical examination is unremarkable except for a few cervical lymph nodes that are palpable. A barium swallow shows a narrowed segment of the cervical esophagus and a proximal esophageal dilatation.
Which of the following is the most likely diagnosis?[/INST]