A 57-year-old man presents with hemoptysis and generalized weakness. His symptoms began with small-volume hemoptysis 4 weeks ago. Over the past 2 weeks, he has become weak and feels "out of it." His appetite has diminished, and he has lost 10 lb of weight. He has a 45-pack-year history of cigarette smoking. Physical examination is unremarkable. Laboratory studies reveal a mild anemia and a serum sodium value of 118 mEq/L. Chest x-ray shows a 5-cm left, mid-lung field mass with widening of the mediastinum suggesting mediastinal lymphadenopathy. MR scan of the brain is unremarkable. What is the most likely cause of his symptoms?
Bronchial carcinoid Adenocarcinoma of the lung Small cell carcinoma of the lung Lung abscess