A 68-year-old female smoker is admitted with progressive weakness, weight loss, and dysphagia. Physical exam: pulse 110 bpm; temperature normal; respirations 18/min; blood pressure 110/60 mm Hg. The patient appears cachectic on general exam. Laboratory data: Hb 9 g/dL; Hct 27%; BUN 13 mg/dL; creatinine 0.4 mg/dL; sodium 124 mEq/L; potassium 3.8 mEq/L. Chest x-rays are shown . An associated symptom that may signal mediastinal involvement and inoperability is