This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
[{'content': 'The staging system for thymoma was developed by: \nSelect and explain. \nA. Masaoka, B. Yokohama, C. Todani, D. Kluive', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The staging system for thymoma was developed by Masaoka The stage is increased on the basis of the degree of invasiveness. The 5-year survival in stage I, 96%; stage II, 86%; stage III, 69%; stage IV, 50%. The French Study Group on Thymic Tumors (GETT) has modified the Masaoka scheme based on the degree of surgical removal. Ref: Harrison, E-18, chapter e-20.', 'role': 'assistant'}]