This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Thorax And Mediastinum, Subject name: Surgery
[{'content': "Pancoast's syndrome is due to:- \nSelect and explain. \nA. C4-5 invasion, B. C8-T1 invasion, C. Lower trunk involvement, D. C5-6 invasion", 'role': 'user'}, {'content': "Answer: B \nExplanation: PANCOAST TUMOR (SUPERIOR SULCUS TUMOR) Pancoast's (or superior sulcus tumor) syndrome results for local extension of a tumor growing in the apex of the lung with involvement of eighth cervical and 1st and 2nd thoracic nerves, with shoulder pain characteristically radiates in the ulnar Often Horner's syndrome and Pancoast's syndrome co-exist", 'role': 'assistant'}]