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
Pancoast's syndrome is due to:- 
Select and explain. 
A. C4-5 invasion, B. C8-T1 invasion, C. Lower trunk involvement, D. C5-6 invasion
B: C8-T1 invasion
Answer: B: C8-T1 invasion 
Explanation: 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