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: Pathology
[{'content': "Gleason's classification used for - \nSelect and explain. \nA. Carcinoma breast, B. Carcinoma prostate, C. Carcinoma pancreas, D. Carcinoma rectum", 'role': 'user'}, {'content': 'Answer: B \nExplanation: Several grading systems have been described for prostatic carcinoma, of which the Gleason system is the best.', 'role': 'assistant'}]