Review Question - QID 109965

A 72-year-old man presents to his primary care physician with weakness. He has felt very weak every morning with his symptoms persisting throughout the day. He notes minor improvement when he rides his bike but otherwise has not noticed any change in his symptoms with rest or ibuprofen use. The patient has lost 12 pounds recently and has had a chronic cough. The patient lives alone and drinks 7 alcoholic beverages per day and smokes 1-2 packs of cigarettes per day for the past 40 years. His temperature is 99.5°F (37.5°C), blood pressure is 177/108 mmHg, pulse is 93/min, respirations are 17/min, and oxygen saturation is 92% on room air. A chest radiograph is ordered as seen in Figure A. Which of the following diagnostic tests would most likely elucidate the cause of this patient's weakness?