<prompt> Which of the following head and neck tumor has the worst prognosis?Adenoid cystic carcinomaAcinic cell carcinomaCystadenolymphomaMucoepidermoid carcinoma  <response>: 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 