This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Salivary Glands, Subject name: Surgery
[{'content': 'All are true about pleomorphic adenoma except:- \nSelect and explain. \nA. Malignant transformation risk is high, B. Mixed tumor, C. Benign tumor, D. Encapsulated', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Risk of malignant transformation is low (3-5%) in pleomorphic adenoma. Malignant mixed tumors include cancers originating from pleomorphic adenomas, termed carcinoma ex pleomorphic adenoma, and de novo malignant mixed tumors. The risk for malignant transformation of benign pleomorphic adenomas is 1.5% within the first 5 years, but risk increases to 9.5% when the benign tumor has been present for more than 15 years.', 'role': 'assistant'}]