A 58-year-old man from Mumbai presents with progressive dyspnea and left-sided pleuritic chest pain for 3 weeks. He has a 40 pack-year smoking history and recent weight loss of 5 kg. On examination, decreased breath sounds and dullness to percussion over the left lung base. Chest X-ray shows a left-sided pleural effusion. Thoracentesis fluid analysis reveals: protein 4.2 g/dL (serum protein 6.8 g/dL), LDH 580 IU/L (serum LDH 420 IU/L), glucose 32 mg/dL, pH 7.1, ADA 8 U/L. Which is the most likely diagnosis?