A 66-year-old male presents with a 5-month history of irritating dry cough and progressive right upper chest pain. Over the past 2 weeks, the pain has radiated to the right shoulder, upper arm, and forearm, accompanied by anhidrosis on the right forehead and difficulty opening the right eye. Physical examination reveals: right miosis, enophthalmos, ptosis, dullness on percussion over the right upper lung, and decreased breath sounds. The rest of the lungs are clear, and the heart shows no abnormalities. Chest X-ray shows a poorly defined mass shadow at the right lung apex. The most likely diagnosis is: