A 50-year-old male presents with left-sided chest pain for 1 month. He has a 20-year history of smoking. Chest X-ray (CXR) shows left pleural effusion with an enlarged left hilar shadow. Pleural fluid analysis: bloody, specific gravity 1.020, protein 30g/L, white blood cell (WBC) count 0.8*10⁹/L (neutrophils 72%, lymphocytes 28%). The most likely diagnosis is: