This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: miscellaneous, Subject name: Pathology
[{'content': 'Which of the following head and neck tumor has the worst prognosis? \nSelect and explain. \nA. Adenoid cystic carcinoma, B. Acinic cell carcinoma, C. Cystadenolymphoma, D. Mucoepidermoid carcinoma', 'role': 'user'}, {'content': "Answer: A \nExplanation: Adenoid Cystic Carcinoma (Cylindroma) This is a highly malignant tumor due to its typical infiltrative nature, especially along the nerve sheaths. Adenoid cystic carcinoma is histologically characterized by cribriform appearance i.e. the epithelial tumor cells of duct-lining and myoepithelial cells are arranged in duct-like structures or masses of cells, having typical fenestrations or cyst-like spaces and hence the name 'adenoid cystic'. These cystic spaces contain PAS-positive basophilic material has a bad prognosis Ref: TEXTBOOK OF PATHOLOGY 6th EDITION - HARSH MOHAN PAGE NO: 537", 'role': 'assistant'}]